bgpd: Add "no listen" socket option for the BGP master configuration

* bgpd.h: add a BGP_OPT_NO_LISTEN option for the master BGP configuration,
  to prevent any listen socket being created automatically. Allows code
  to be used outside of BGP daemon settings.
* bgpd.c: (bgp_get) honour above the flag, suppress auto-creation of listen
  socket on first BGP instance if set.
  (bgp_option_set) whitelist BGP_OPT_NO_LISTEN
2 files changed