carp support into GENERIC

[Corey Smith]

Please CC: me as I'm not on list.

Please consider adding "device carp" to the GENERIC kernel. We have
many servers using carp and it increases the complexity of installs
and (freebsd-update) upgrades when you have to build a custom kernel
only for this functionality. The kernel size increase is small and the
benefits are (IMHO) worthwhile.

device carp is not in the GENERIC kernel and (AFAIK) it is very
difficult to make a module to add this support via kld.  carp is also
enabled by default in OpenBSD.

-Corey Smith