FSDP full precision `model.eval` silently failing 
Labels: triaged, module: fsdp

### 🐛 Describe the bug

I'm calling `model.eval()` on an FSDP wrapped model to evaluate performance in full precision. Some parameters are not getting cast properly, leading to incorrect results (but no errors). 

### Fix that works: 
Traversing the `wrapped_model.named_modules()` and setting `module.train(False)` on the correct modules (prone to breakage)

### Fix that doesn't work but may be illuminating in debugging: 
Traversing the wrapped module and calling `module.train(False)` instead of calling `wrapped_model.eval()` makes the failure not silent: `F.scaled_dot_product_attention` throws an error that it got inputs of fp32 but expected inputs of bf16. Specifically, calling `module.train(False)` on the module that is the block for FSDP wrapping causes the break.

### Versions

Collecting environment information...
PyTorch version: 2.1.0.dev20230609+cu118
Is debug build: False
CUDA used to build PyTorch: 11.8
ROCM used to build PyTorch: N/A

OS: Ubuntu 20.04.6 LTS (x86_64)
GCC version: (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0
Clang version: Could not collect
CMake version: version 3.25.0
Libc version: glibc-2.31

Python version: 3.8.16 (default, Mar  2 2023, 03:21:46)  [GCC 11.2.0] (64-bit runtime)
Python platform: Linux-5.15.0-1035-oracle-x86_64-with-glibc2.17
Is CUDA available: True
CUDA runtime version: Could not collect
CUDA_MODULE_LOADING set to: LAZY
GPU models and configuration:
GPU 0: NVIDIA A100-SXM4-40GB
GPU 1: NVIDIA A100-SXM4-40GB
GPU 2: NVIDIA A100-SXM4-40GB
GPU 3: NVIDIA A100-SXM4-40GB
GPU 4: NVIDIA A100-SXM4-40GB
GPU 5: NVIDIA A100-SXM4-40GB
GPU 6: NVIDIA A100-SXM4-40GB
GPU 7: NVIDIA A100-SXM4-40GB

Nvidia driver version: 515.105.01
cuDNN version: Probably one of the following:
/usr/lib/x86_64-linux-gnu/libcudnn.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_adv_infer.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_adv_train.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_cnn_infer.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_cnn_train.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_ops_infer.so.8.9.1
/usr/lib/x86_64-linux-gnu/libcudnn_ops_train.so.8.9.1
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True

CPU:
Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   48 bits physical, 48 bits virtual
CPU(s):                          256
On-line CPU(s) list:             0-127
Off-line CPU(s) list:            128-255
Thread(s) per core:              1
Core(s) per socket:              64
Socket(s):                       2
NUMA node(s):                    8
Vendor ID:                       AuthenticAMD
CPU family:                      25
Model:                           1
Model name:                      AMD EPYC 7J13 64-Core Processor
Stepping:                        1
Frequency boost:                 enabled
CPU MHz:                         2550.000
CPU max MHz:                     3673.0950
CPU min MHz:                     1500.0000
BogoMIPS:                        4899.83
Virtualization:                  AMD-V
L1d cache:                       4 MiB
L1i cache:                       4 MiB
L2 cache:                        64 MiB
L3 cache:                        512 MiB
NUMA node0 CPU(s):               0-15
NUMA node1 CPU(s):               16-31
NUMA node2 CPU(s):               32-47
NUMA node3 CPU(s):               48-63
NUMA node4 CPU(s):               64-79
NUMA node5 CPU(s):               80-95
NUMA node6 CPU(s):               96-111
NUMA node7 CPU(s):               112-127
Vulnerability Itlb multihit:     Not affected
Vulnerability L1tf:              Not affected
Vulnerability Mds:               Not affected
Vulnerability Meltdown:          Not affected
Vulnerability Mmio stale data:   Not affected
Vulnerability Retbleed:          Not affected
Vulnerability Spec store bypass: Vulnerable
Vulnerability Spectre v1:        Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
Vulnerability Spectre v2:        Vulnerable, IBPB: disabled, STIBP: disabled, PBRSB-eIBRS: Not affected
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f1
6c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 invpcid_single hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt
 xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd amd_ppin arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid overflow_recov succor smca fsrm

Versions of relevant libraries:
[pip3] numpy==1.24.1
[pip3] pytorch-triton==2.1.0+9820899b38
[pip3] torch==2.1.0.dev20230609+cu118
[pip3] torchaudio==2.1.0.dev20230609+cu118
[pip3] torchvision==0.16.0.dev20230609+cu118
[pip3] triton==2.0.0
[conda] numpy                     1.24.1                   pypi_0    pypi
[conda] pytorch-triton            2.1.0+9820899b38          pypi_0    pypi
[conda] torch                     2.1.0.dev20230609+cu118          pypi_0    pypi
[conda] torchaudio                2.1.0.dev20230609+cu118          pypi_0    pypi
[conda] torchvision               0.16.0.dev20230609+cu118          pypi_0    pypi
[conda] triton                    2.0.0                    pypi_0    pypi

cc @zhaojuanmao @mrshenli @rohan-varma @awgu