rescue: add ipfw, pfctl

Rationale for this change:

• ipf is already there

• if the kernel is configured with a packet filter which drops packets by default, pfctl or ipfw will be required in the rescue environment to make the network functional.

• rescue's stated purpose is to be useful for small/embedded systems (and is also quite useful for small jails); a rescue-based router would want these binaries.

On amd64, this increases the size of rescue from 17346200 to 17907248,
or 561048 bytes (3.2%).

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1169