Add operators =, !=, - (range), >< (exclsive range) to the as-path

filters (AS, peer-as, source-as, transit-as).
Add a use case (block illegal AS numbers) to the bgpd.conf example.
feedback from claudio, sthen, florian,
ok florian@ phessler@

src/etc/examples/bgpd.conf

@@ -1,4 +1,4 @@
-# $OpenBSD: bgpd.conf,v 1.3 2015/09/11 18:59:00 sthen Exp $
+# $OpenBSD: bgpd.conf,v 1.4 2016/06/03 17:36:37 benno Exp $
 # sample bgpd configuration file
 # see bgpd.conf(5)
 
@@ -119,3 +119,14 @@ deny from any prefix fc00::/7 prefixlen >= 7		# unique local unicast
 deny from any prefix fe80::/10 prefixlen >= 10		# link local unicast
 deny from any prefix fec0::/10 prefixlen >= 10		# old site local unicast
 deny from any prefix ff00::/8 prefixlen >= 8		# multicast
+
+# filter bogon AS numbers
+# http://www.iana.org/assignments/as-numbers/as-numbers.xhtml
+deny from any AS 23456				# AS_TRANS
+deny from any AS 64496 - 64511			# Reserved for use in docs and code RFC5398
+deny from any AS 64512 - 65534			# Reserved for Private Use RFC6996
+deny from any AS 65535				# Reserved RFC7300
+deny from any AS 65536 - 65551			# Reserved for use in docs and code RFC5398 
+deny from any AS 65552 - 131071			# Reserved
+deny from any AS 4200000000 - 4294967294	# Reserved for Private Use RFC6996
+deny from any AS 4294967295			# Reserved RFC7300