Do not strip outer header when operating in transport mode.
Instead requeue mbuf back to IPv4 protocol handler. If there is one extra IP-IP
encapsulation, it will be handled with tunneling interface. And thus proper
interface will be exposed into mbuf's rcvif. Also, tcpdump that listens on tunneling
interface will see packets in both directions.

Sponsored by:	Yandex LLC


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272394 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f