Add (again) support for divert sockets. They allow you to:

- queue packets from pf(4) to a userspace application
- reinject packets from the application into the kernel stack.
The divert socket can be bound to a special "divert port" and will
receive every packet diverted to that port by pf(4).
The pf syntax is pretty simple, e.g.:
pass on em0 inet proto tcp from any to any port 80 divert-packet port 1
A lot of discussion have happened since my last commit that resulted
in many changes and improvements.
I would *really* like to thank everyone who took part in the discussion
especially canacar@ who spotted out which are the limitations of this approach.
OpenBSD divert(4) is meant to be compatible with software running on
top of FreeBSD's divert sockets even though they are pretty different and will
become even more with time.
discusses with many, but mainly reyk@ canacar@ deraadt@ dlg@ claudio@ beck@
tested by reyk@ and myself
ok reyk@ claudio@ beck@
manpage help and ok by jmc@

src/etc/protocols

@@ -1,7 +1,7 @@
 #
 # Internet (IP) protocols
 #
-#	$OpenBSD: protocols,v 1.21 2004/05/07 16:27:23 henning Exp $
+#	$OpenBSD: protocols,v 1.22 2009/10/04 16:08:37 michele Exp $
 #
 # Updated based on RFC 1340, Assigned Numbers (July 1992).
 # See also http://www.iana.org/assignments/protocol-numbers
@@ -142,3 +142,4 @@ fc	133	FC		# Fibre Channel
 rsvp-e2e-ignore	134	RSVP-E2E-IGNORE
 pfsync	240	PFSYNC		# PF Synchronization
 reserved 255	Reserved	#
+divert	258	DIVERT		# Divert pseudo-protocol [non IANA]