enabling bridge_ipf

[Maxime Villard <max%m00nbsd.net@localhost>]

Any reason this isn't enabled by default? Right now you need to recompile
your kernel with "options BRIDGE_IPF" if you want a firewall on the bridge.
This is annoying.

There is already a dynamic switch behind it anyway: you need to pass "ipf"
to brconfig in order for filtering to actually be enabled, so having the
extra "options BRIDGE_IPF" serves little purpose.

I want to enable BRIDGE_IPF by default, by removing the option and the
#ifdefs. That is, by making the code part of bridge(4) by default.

Note that BRIDGE_IPF is not related to IPF. It uses the pfil interface, so
it works with NPF.

Maxime