Merge r250802 from bryanv/vtnetmq - Fix setting of the Rx filters

QEMU 1.4 made the descriptor requirement stricter - the size of buffer
descriptor must exactly match the number of MAC addresses provided.

PR:		kern/178955
MFC after:	5 days
Internalise handling of virtualised hook points inside
hhook_{add|remove}_hook_lookup() so that khelp (and other potential API
consumers) do not have to care when they attempt to (un)hook a particular hook
point identified by id and type.

Reviewed by:	scottl
MFC after:	1 week