chgsbsize: Optimize for x86_64 by avoid uidinfo spinlock

This kills one of the highly contended spinlocks on accept(2) path.  And
it also greatly helps connect(2) path.

With this commit, tools/kq_connect_client could do 273Kconns/s instead
of 260Kconns/s (~5% improvement, however, connect(2) is still cpu bound).
kernel: Comment out old or yet unsupported USB devices in our configs.
LINT/LINT64: Fix umass comment.