Move memset under ifdef INET6.

MFH:		1 month
Reported by:	bz


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273090 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Add more ifdefs. SIOC*_IN6 are defined only with INET6.

MFC after:	1 month
Reported  by:	bz


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273091 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
opt_mrouting.h isn't needed anymore.

MFC after:	1 month


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273092 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f