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/bgp_attr.h b/bgpd/bgp_attr.h
index 8457f40..9ff074b 100644
--- a/bgpd/bgp_attr.h
+++ b/bgpd/bgp_attr.h
@@ -66,6 +66,9 @@
 
   /* Extended Communities attribute. */
   struct ecommunity *ecommunity;
+
+  /* Large Communities attribute. */
+  struct lcommunity *lcommunity;
   
   /* Route-Reflector Cluster attribute */
   struct cluster_list *cluster;