bgpd: code cleanup

* bgpd/bgp_aspath.c
  * ashash: only used in one file, make static
  * aspath_count_numas(): dead code, sayonara
* bgpd/bgpd.c
  * peer_nsf_stop(): only used in one file, make static
* bgpd/bgp_packet.h
  * bgp_capability_receive(): add missing prototype for a
    global function
diff --git a/bgpd/bgpd.c b/bgpd/bgpd.c
index b34f996..cf3a6b4 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -1129,7 +1129,7 @@
   return 0;
 }
 
-void
+static void
 peer_nsf_stop (struct peer *peer)
 {
   afi_t afi;