Pass mbuf to pfil processing before stripping outer IP header as it
is described in if_enc(4).

MFC after:	2 week
Sponsored by:	Yandex LLC


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274230 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f