Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add a very simple IPDIVERT test, which creates IP divert sockets and
checks for collision/non-collision properties in binding them. This
test would have identified a bug recently reported on current@
involding my disaggregation of the pcbinfo lock.

It would be nice if this test also exercised packet diversion and
injection, but that is for another day.

MFC after: 3 days
Sponsored by: Juniper Networks, Inc.