ip_mfilter_alloc
imf = ip_mfilter_alloc(M_NOWAIT, MCAST_UNDEFINED, MCAST_INCLUDE);
imf = ip_mfilter_alloc(M_NOWAIT, MCAST_UNDEFINED, MCAST_EXCLUDE);
struct in_mfilter *ip_mfilter_alloc(int mflags, int st0, int st1);
imf = ip_mfilter_alloc(M_WAITOK, 0, 0);
imf = ip_mfilter_alloc(M_WAITOK, 0, 0);