After r221249 allow SCTP to be compiled in an IPv6 only environment as well.
After r221249 allow SCTP to be compiled in an IPv6 only environment as well.

Sponsored by:	The FreeBSD Foundation
Sponsored by:	iXsystems
MFC after:	10 days

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