This is a direct commit to the stable/10 branch. This would have been

This is a direct commit to the stable/10 branch. This would have been
MFC r340754 except that etc/rc.d has been moved in HEAD which would
have resulted in a tree conflict if merged.

Allow forced start of ipmon in special cases where testing is desired
(or other special cases) and when ipfilter is disabled in rc.conf but
started by other means.

git-svn-id: svn://svn.freebsd.org/base/stable/10@341289 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f