MFC r196932:

MFC r196932:

When joining a multicast group, the inp_lookup_mcast_ifp call
does a KASSERT that the group address is multicast, so the
check if this is indeed true and eventually return a EINVAL if not,
should be done before calling inp_lookup_mcast_ifp. This fixes a kernel
crash when calling setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,...)
with invalid group address.

Reviewed by:	bms
Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@197089 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f