bgpd: rename SAFI 3 according to RFC4760

- SAFI value 3 is reserved.  It was assigned by RFC 2858 for a use
  that was never fully implemented, so it is deprecated by this
  document.

* zebra.h: rename macro
* bgp_fsm.c: (bgp_graceful_restart_timer_expire,
  bgp_graceful_stale_timer_expire, bgp_stop, bgp_establish): update
* bgpd.c: (peer_nsf_stop): update
* bgp_open.c: (bgp_capability_vty_out): SAFI 3 isn't a recognized case
  any more
diff --git a/bgpd/bgp_fsm.c b/bgpd/bgp_fsm.c
index 487ebdd..813e59e 100644
--- a/bgpd/bgp_fsm.c
+++ b/bgpd/bgp_fsm.c
@@ -355,7 +355,7 @@
 
   /* NSF delete stale route */
   for (afi = AFI_IP ; afi < AFI_MAX ; afi++)
-    for (safi = SAFI_UNICAST ; safi < SAFI_UNICAST_MULTICAST ; safi++)
+    for (safi = SAFI_UNICAST ; safi < SAFI_RESERVED_3 ; safi++)
       if (peer->nsf[afi][safi])
 	bgp_clear_stale_route (peer, afi, safi);
 
@@ -388,7 +388,7 @@
 
   /* NSF delete stale route */
   for (afi = AFI_IP ; afi < AFI_MAX ; afi++)
-    for (safi = SAFI_UNICAST ; safi < SAFI_UNICAST_MULTICAST ; safi++)
+    for (safi = SAFI_UNICAST ; safi < SAFI_RESERVED_3 ; safi++)
       if (peer->nsf[afi][safi])
 	bgp_clear_stale_route (peer, afi, safi);
 
@@ -481,7 +481,7 @@
 	  UNSET_FLAG (peer->sflags, PEER_STATUS_NSF_MODE);
 
 	  for (afi = AFI_IP ; afi < AFI_MAX ; afi++)
-	    for (safi = SAFI_UNICAST ; safi < SAFI_UNICAST_MULTICAST ; safi++)
+	    for (safi = SAFI_UNICAST ; safi < SAFI_RESERVED_3 ; safi++)
 	      peer->nsf[afi][safi] = 0;
 	}
 
@@ -799,7 +799,7 @@
   /* graceful restart */
   UNSET_FLAG (peer->sflags, PEER_STATUS_NSF_WAIT);
   for (afi = AFI_IP ; afi < AFI_MAX ; afi++)
-    for (safi = SAFI_UNICAST ; safi < SAFI_UNICAST_MULTICAST ; safi++)
+    for (safi = SAFI_UNICAST ; safi < SAFI_RESERVED_3 ; safi++)
       {
 	if (peer->afc_nego[afi][safi]
 	    && CHECK_FLAG (peer->cap, PEER_CAP_RESTART_ADV)