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/bgpd.c b/bgpd/bgpd.c
index ee0cc5d..e803855 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -1147,7 +1147,7 @@
   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;
 
   if (peer->t_gr_restart)