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

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

Add an ifconfig carp option that enables users to set
the state of the carp cluster.

This is a direct commit to stable/9 because -HEAD's
code is very different. I discussed this with Gleb
and the reason for this is that since we do not
touch the kernel itself and are not adding very
weird or confusing things, we can commit this to the
stable branch directly.

The options 'master' and 'backup' are now available,
which enables the administrator to force a node into
the backup or master state on the cluster. Ofcourse
preempt has to be disabled otherwise the master node
will become master again.

One can do that with:

sysctl net.inet.carp.preempt=0

After that one can schedule maintenance on the node
normally running as the master and such.

PR: 100956
Discussed with: glebius
MFC after: 1 weeks

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

Approved by: re (implicit)

Shortening a passphrase caused wrong authentication key to be used.
Fix this in a FreeBSD and OpenBSD compatible way.

MFC after: 3 days

Use afswch->af_other_status for carp_status() and pfsync_status().

Sponsored by: Rambler

Add CARP (Common Address Redundancy Protocol), which allows multiple
hosts to share an IP address, providing high availability and load
balancing.

Original work on CARP done by Michael Shalayeff, with many
additions by Marco Pfatschbacher and Ryan McBride.

FreeBSD port done solely by Max Laier.

Patch by: mlaier
Obtained from: OpenBSD (mickey, mcbride)