A recent commit (1.131.2.13) removed the security fix associated with
FreeBSD-SA-01:08, breaking the "established" TCP matching flag even
more than it was prior to the security advisory. Reinstate the fix by
restoring the conditional assocated with entering tcpflg_match().

Reported by a number of people via send-pr, security-officer,
et al., including:

Steven Farmer <steve@megahack.com>
Bernd Luevelsmeyer <bdluevel@heitec.net>
Andrew Gordon <arg@arg1.demon.co.uk>

Thanks to those people for bringing this to our attention in such a
timely manner. An updated advisory and/or announcement to the
freebsd-stable mailing list will be forthcoming, once all parties have
confirmed that this resolves the problems they were experiencing.

PR: 24833
Approved by: security-officer
Slap on the wrist to: luigi