kevent(2): Note DOOMED vnodes with NOTE_REVOKE

In poll mode, check for and wake VBAD vnodes. (Vnodes that are VBAD at
registration will never be woken by the RECLAIM trigger.)

Add post-VOP_RECLAIM hook to trigger notes on vnode reclamation. (Vnodes that
were fine at registration but are vgoned while being monitored should signal
waiters.)

Reviewed by: kib
Approved by: markj (mentor)
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D3675