Introduce kern.timecounter.smp_tsc_adjust tunable (disabled by default) and
respective functionality, allowing to synchronize TSC on APs to match BSP's
during boot.  It may be unsafe in general case due to theoretical chance of
later drift if CPUs are using different clock rate or source, but it allows
to use TSC in some cases when difference caused by some initialization bug,
while TSCs are known to increment synchronously.

Reviewed by:	jimharris, kib
MFC after:	1 month
cxgbe/tom: Update the CLIP table on the chip when there are changes
to the list of IPv6 addresses on the system.  The table is used for
TOE+IPv6 only.
Recover missing arp_ifinit() call.

MFC after:	2 weeks
cxgbe(4): Refuse to install T5 firmwares on a T4 card (and vice versa).

MFC after:	1 week
When an NFS unmount occurs, once vflush() writes the last dirty
buffer for the last vnode on the mount back to the server, it
returns. At that point, the code continues with the unmount,
including freeing up the nfs specific part of the mount structure.
It is possible that an nfsiod thread will try to check for an
empty I/O queue in the nfs specific part of the mount structure
after it has been free'd by the unmount. This patch avoids this problem by
setting the iodmount entries for the mount back to NULL while holding the
mutex in the unmount and checking the appropriate entry is non-NULL after
acquiring the mutex in the nfsiod thread.

Reported and tested by:	pho
Reviewed by:	kib
MFC after:	2 weeks
Attempt to mitigate poor initialization of arc4 by one-shot
reinitialization from yarrow right after good entropy is harvested.

Approved by:    secteam (delphij)
MFC after:      1 week
Fix the symlink creation from r249484 so that repeated
installs work correctly.

Suggested by Tijl Coosemans.
An even more refined version of r249484, until we can come up with
a good fix for the -print-file-name=include breakage.

As suggested by Andrey Chernov.