Disable Intel I/OAT DMA support

Intel IOAT is a obsolete feature, which can't improve
performance visible, even we ever encountered kernel
panic due to a bug in its driver.

So we try to disable it now.
Bypass GSO on packets from tc action mirred module.

mirred module may redirect ingress packets to tx path, this will
break some assertions if we enable GSO for such packets, which
results in a lot of kernel warnings and poor performance.
io_latency: add io_latency.h 

include/linux/io_latency.h contains iolatency related structure/function
definitions.

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
io_latency: add iolatency stats in block/scsi layer

1. Extend struct request and request_queue to contain iolatency related field
2. do iolatency stats in get_request_wait()/blk_finish_request()/scsi_dispatch_cmd()

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
io_latency: export proc interface

Add proc interface for iolatency under /proc/io-latency/sdX. There're 3
entries controlling the behavior of iolatency:
1. enable_iolatency: disable/enable the RT stats for LLD/device
2. enable_soft_iolatency: disable/enable the RT stats for software
layer(mainly cost in block and scsi layer)
3. enable_use_us: diable/enable millisecond-level stats. Notice that it
can only be modified when enable_iolatency=0 and enable_soft_iolatency=0

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Merge pull request #50 from shazj99/iolatency

Add Iolatency

Thanks, Applied.
Merge pull request #47 from Rover-Yu/dev

two networking subsystem pull requests on dev branch