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
4 files changed