bgpd: Add support for BGP Large Communities

As described by Michael Lambert <lambert@psc.edu>  to the list:

  Traditional communities are four-octet entities to support two-octet ASNs
  and are usually represented as <asn>:<data>.  Large communities are an
  enhancement to support four-octet ASNs and are 12 octets long, represented
  as <asn>:<data-1>:<data-2>.

  This issue has been tracked in quagga bugzilla ticket #875, which documents
  some of the usage and indicates that some testing has been done.

TODO: Documentation - update doc/bgpd.texi.

* bgp_attr.{c,h}: Add BGP_ATTR_LARGE_COMMUNITIES codepoint. Add
  (struct lcommunity *) to (struct bgp_attr_extra).
* bgp_clist.{c,h}: Large community codepoints and routines.
* bgp_route.c: Display support.
* bgp_routemap.c: 'match lcommunity', 'set large-community' and
  'set large-comm-list'
* bgp_vty.c: Peer configuration, add 'large' to 'neighbor send-community ..'.
  Add "show ip bgp large-community", ""ip large-community-list ...".

Authors: Keyur Patel <keyur@arrcus.com>
         Job Snijders <job@instituut.net>
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index a6cc34e..c2df672 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -425,6 +425,7 @@
 #define PEER_FLAG_MAX_PREFIX_WARNING        (1 << 15) /* maximum prefix warning-only */
 #define PEER_FLAG_NEXTHOP_LOCAL_UNCHANGED   (1 << 16) /* leave link-local nexthop unchanged */
 #define PEER_FLAG_NEXTHOP_SELF_ALL          (1 << 17) /* next-hop-self all */
+#define PEER_FLAG_SEND_LARGE_COMMUNITY      (1 << 18) /* Send large Communities */
 
   /* MD5 password */
   char *password;
@@ -655,6 +656,7 @@
 #define BGP_ATTR_AS4_AGGREGATOR                 18
 #define BGP_ATTR_AS_PATHLIMIT                   21
 #define BGP_ATTR_ENCAP                          23
+#define BGP_ATTR_LARGE_COMMUNITIES              32
 
 /* BGP update origin.  */
 #define BGP_ORIGIN_IGP                           0