unbreak configurations using carppeers

unbreak configurations using carppeers

ip_carp.c r1.322 removed the ability to receive carp protocol packets
on !IFT_CARP interfaces. however, carppeers cause the carp protocol
packets to be directed to a unicast address on another interface,
which definitely is not mapped back to a carp interface.

this brings back the ability to get carp packets on parent interfaces.
it is a bit different to a backout because it only allows carp
parents to be ethernet interfaces.

mpi@ told me carp regress tests were failing.