Add rwlock to struct dadq.  A panic could occur when a large number of
addresses performed DAD at the same time.
In uart_bus_grab(), use the ier_mask instead of a custom hack for XScale.

Suggested by:	jmg
Change examples to have master skew above 0 to have ability to overwrite this
from the slave (for example, when master is failing on disk IO and could not be
logged into or execute cronjob).

Commented out examples changed too to simplify future merging.

Idea by:	kaa@zvuki.ru
Discussed with:	glebius
MFC after:	1 week
Fix unintended KBI change from r264905.  Add _fib versions of
ifa_ifwithnet() and ifa_ifwithdstaddr()  The legacy functions will call the
_fib() versions with RT_ALL_FIBS, preserving legacy behavior.

sys/net/if_var.h
sys/net/if.c
	Add legacy-compatible functions as described above.  Ensure legacy
	behavior when RT_ALL_FIBS is passed as fibnum.

sys/netinet/in_pcb.c
sys/netinet/ip_output.c
sys/netinet/ip_options.c
sys/net/route.c
sys/net/rtsock.c
sys/netinet6/nd6.c
	Call with _fib() functions if we must use a specific fib, or the
	legacy functions otherwise.

tests/sys/netinet/fibs_test.sh
tests/sys/netinet/udp_dontroute.c
	Improve the udp_dontroute test.  The bug that this test exercises is
	that ifa_ifwithnet() will return the wrong address, if multiple
	interfaces have addresses on the same subnet but with different
	fibs.  The previous version of the test only considered one possible
	failure mode: that ifa_ifwithnet_fib() might fail to find any
	suitable address at all.  The new version also checks whether
	ifa_ifwithnet_fib() finds the correct address by checking where the
	ARP request goes.

Reported by:	bz, hrs
Reviewed by:	hrs
MFC after:	1 week
X-MFC-with:	264905
Sponsored by:	Spectra Logic
Update size in vt_grow if we don't have to reallocate

vt_grow may be called with a new size that's larger than previous but
does not require reallocation - for example, when the number of columns
is the same and new number of rows is less than the history size.
Prior to this change we would fail to update vb_scr_size, and then hit
a KASSERT when trying to write to the newly visible rows.

Sponsored by:	The FreeBSD Foundation