Add an additional routing table lookup when m->m_pkthdr.fibnum is changed
at a PFIL hook in ip{,6}_output().  IPFW setfib rule did not perform
a routing table lookup when the destination address was not changed.

CR:	D805


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272391 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f