bgpd: Add new configuration cli for graceful restart.

There is support to configure graceful restart timer. This is the
time to wait to delete stale routes before a BGP open message is
received.

bgp graceful-restart restart-time <1-3600>
no bgp graceful-restart [<1-255>]

* bgpd/bgp_vty.c
  * Define command strings for above CLI
* bgpd/bgpd.c
  * bgp_config_write(): Output graceful restart-time configuration

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Tested-by: NetDEF CI System <cisystem@netdef.org>
diff --git a/bgpd/bgpd.c b/bgpd/bgpd.c
index 3517011..e86665b 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -5484,6 +5484,9 @@
       if (bgp->stalepath_time != BGP_DEFAULT_STALEPATH_TIME)
 	vty_out (vty, " bgp graceful-restart stalepath-time %d%s",
 		 bgp->stalepath_time, VTY_NEWLINE);
+      if (bgp->restart_time != BGP_DEFAULT_RESTART_TIME)
+	vty_out (vty, " bgp graceful-restart restart-time %d%s",
+		 bgp->restart_time, VTY_NEWLINE);
       if (bgp_flag_check (bgp, BGP_FLAG_GRACEFUL_RESTART))
        vty_out (vty, " bgp graceful-restart%s", VTY_NEWLINE);