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_lcommunity.h b/bgpd/bgp_lcommunity.h
new file mode 100644
index 0000000..7841b4b
--- /dev/null
+++ b/bgpd/bgp_lcommunity.h
@@ -0,0 +1,75 @@
+/* BGP Large Communities Attribute.
+
+Copyright (C) 2016 Keyur Patel <keyur@arrcus.com>
+
+This file is part of GNU Zebra.
+
+GNU Zebra is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 2, or (at your option) any
+later version.
+
+GNU Zebra is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Zebra; see the file COPYING.  If not, write to the Free
+Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+02111-1307, USA.  */
+
+#ifndef _QUAGGA_BGP_LCOMMUNITY_H
+#define _QUAGGA_BGP_LCOMMUNITY_H
+
+/* Extended communities attribute string format.  */
+#define LCOMMUNITY_FORMAT_ROUTE_MAP            0
+#define LCOMMUNITY_FORMAT_COMMUNITY_LIST       1
+#define LCOMMUNITY_FORMAT_DISPLAY              2
+
+/* Large Communities value is twelve octets long.  */
+#define LCOMMUNITY_SIZE                        12
+
+/* Large Communities attribute.  */
+struct lcommunity
+{
+  /* Reference counter.  */
+  unsigned long refcnt;
+
+  /* Size of Extended Communities attribute.  */
+  int size;
+
+  /* Extended Communities value.  */
+  u_int8_t *val;
+
+  /* Human readable format string.  */
+  char *str;
+};
+
+/* Extended community value is eight octet.  */
+struct lcommunity_val
+{
+  char val[LCOMMUNITY_SIZE];
+};
+
+#define lcom_length(X)    ((X)->size * LCOMMUNITY_SIZE)
+
+extern void lcommunity_init (void);
+extern void lcommunity_finish (void);
+extern void lcommunity_free (struct lcommunity **);
+extern struct lcommunity *lcommunity_parse (u_int8_t *, u_short);
+extern struct lcommunity *lcommunity_dup (struct lcommunity *);
+extern struct lcommunity *lcommunity_merge (struct lcommunity *, struct lcommunity *);
+extern struct lcommunity *lcommunity_uniq_sort (struct lcommunity *);
+extern struct lcommunity *lcommunity_intern (struct lcommunity *);
+extern int lcommunity_cmp (const void *, const void *);
+extern void lcommunity_unintern (struct lcommunity **);
+extern unsigned int lcommunity_hash_make (void *);
+extern struct hash *lcommunity_hash (void);
+extern struct lcommunity *lcommunity_str2com (const char *);
+extern char *lcommunity_lcom2str (struct lcommunity *, int);
+extern int lcommunity_match (const struct lcommunity *, const struct lcommunity *);
+extern char *lcommunity_str (struct lcommunity *);
+extern int lcommunity_include (struct lcommunity *lcom, u_char *ptr);
+extern void lcommunity_del_val (struct lcommunity *lcom, u_char *ptr);
+#endif /* _QUAGGA_BGP_LCOMMUNITY_H */