Fix hangs in a uniprocessor configuration (qemu, virtualbox, real hw).

sys/net/iflib.c:

Add ctx to filter_info and don't skpi interrupt early on unless we're on an
SMP system

sys/kern/subr_gtaskqueue.c:

Skip smp check if we're running UP

Submitted by: Matt Macy <mmacy@nextbsd.org>
Reported by: emaste bde