bgpd: Add new configuration cli for eBGP and iBGP multipath.
There is support to configure this for each (AFI,SAFI), but
currently this configuration is only present for IPv4 unicast:

 maximum-paths [ibgp] <1-255>
 no maximum-paths [ibgp] [<1-255>]

* bgpd/Makefile.am
  * Add bgp_mpath.h and bgp_mpath.c to build
* bgpd/bgp_mpath.h
  * New file for bgp multipath declarations
  * define BGP_DEFAULT_MAXPATHS
* bgpd/bgp_mpath.c
  * bgp_maximum_paths_set(): Configure maximum paths for the given
    afi, safi and bgp instance
  * bgp_maximum_paths_unset(): Return maximum paths configuration to
    the default setting for the given afi, safi and bgp instance
* bgpd/bgp_vty.c
  * Define command strings for above CLI
  * bgp_config_write_maxpaths(): Outputs configuration for the given
    afi, safi and bgp instance
  * Install command elements for IPv4 unicast
* bgpd/bgp_zebra.h
  * bgp_config_write_maxpaths(): External declaration
* bgpd/bgpd.c
  * bgp_create(): Initialize bgp instance to default maximum paths setting
  * bgp_config_write_family(): Output maximum paths configuration
    for the given address family
  * bgp_config_write(): Output maximum paths configuration for
    IPv4 unicast address family
* bgpd/bgpd.h
  * struct bgp: Add storage for maximum paths configuration for
    each afi, safi
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index 4da19e7..bd03f65 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -162,6 +162,12 @@
   /* BGP graceful restart */
   u_int32_t restart_time;
   u_int32_t stalepath_time;
+
+  /* Maximum-paths configuration */
+  struct bgp_maxpaths_cfg {
+    u_int16_t maxpaths_ebgp;
+    u_int16_t maxpaths_ibgp;
+  } maxpaths[AFI_MAX][SAFI_MAX];
 };
 
 /* BGP peer-group support. */