Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

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.