Virtualize the pfil hooks so that different jails may chose different
packet filters. ALso allows ipfw to be enabled on on ejail and disabled
on another. In 8.0 it's a global setting.
and
Unbreak the VIMAGE build with IPSEC, broken with r197952 by
virtualizing the pfil hooks.
For consistency add the V_ to virtualize the pfil hooks in here as well.