- Fix LOCAL_MTREE so it properly handles multiple files and quotes
  its value into submakes

PR:		conf/179466
Submitted by:	Garrett Cooper <yaneurabeya@gmail.com>
Approved by:	bapt
MFC after:	2 weeks
Sponsored by:	EMC / Isilon Storage Division
Implement support for rx buffer packing.  Enable it by default for T5
cards.

This is a T4 and T5 chip feature which lets the chip deliver multiple
Ethernet frames in a single buffer.  This is more efficient within the
chip, in the driver, and reduces wastage of space in rx buffers.

- Always allocate rx buffers from the jumbop zone, no matter what the
  MTU is.  Do not use the normal cluster refcounting mechanism.
- Reserve space for an mbuf and a refcount in the cluster itself and let
  the chip DMA multiple frames in the rest.
- Use the embedded mbuf for the first frame and allocate mbufs on the
  fly for any additional frames delivered in the cluster.  Each of these
  mbufs has a reference on the underlying cluster.
If reading a virtual-device value fails, attempt to read a virtual-device-ext
value.  Some hosts do not publish "extended" disk IDs via virtual-device in
an attempt to avoid confusing old blkfront drivers, and without this change
we failed to attach such disks.

In particular, this commit allows all 24 ephemeral disks on EC2 hs1.8xlarge
instances to be used, instead of only the first 15.

MFC after:	3 days
Fix the sysctl that displays whether buffer packing is enabled
or not.