MFC r270348:

MFC r270348:
Add some missing checks for unsupported interfaces (e.g. pflog(4)) when
handling ioctls. While here, remove duplicated checks for a NULL ifp in
in6_control(): this check is already done near the beginning of the
function.

MFC r270349:
Suppress warnings when retrieving protocol stats from interfaces that
don't support IPv6 (e.g. pflog(4)).

PR:	189117

git-svn-id: svn://svn.freebsd.org/base/stable/9@271184 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f