Test if the interface is afif in dhcpif() and syncdhcpif(), as done in ipv6_autoconfif.
Test if the interface is afif in dhcpif() and syncdhcpif(), as
done in ipv6_autoconfif.

Reviewed by:	hrs (freebsd-rc@)
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase