Fixes to RFC2385/MD5 BGP

* bgpd/bgp_network.c: Fix MD5 listen in IPv4 version of bgp_socket() by
  adding listen socket to listen_sockets list so that MD5 passwords can
  get set.
* lib/sockopt.c: (sockopt_tcp_signature) Fix bogus "% Error while applying
  TCP-Sig to session(s)" / "can't set TCP_MD5SIG option" startup error
  messages by not returning error when there isn't one.
diff --git a/bgpd/bgp_network.c b/bgpd/bgp_network.c
index 6d16c6e..99f7113 100644
--- a/bgpd/bgp_network.c
+++ b/bgpd/bgp_network.c
@@ -517,6 +517,7 @@
       return ret;
     }
 
+  listnode_add (bm->listen_sockets, (void *)sock);
   thread_add_read (bm->master, bgp_accept, bgp, sock);
 
   return sock;
diff --git a/lib/sockopt.c b/lib/sockopt.c
index 96324ff..55c6226 100644
--- a/lib/sockopt.c
+++ b/lib/sockopt.c
@@ -550,8 +550,8 @@
       if (su2->sa.sa_family == AF_INET)
         {
           sockunion_free (susock);
-          return -1;
-        };
+          return 0;
+        }
       
 #ifdef HAVE_IPV6
       /* If this does not work, then all users of this sockopt will need to
@@ -580,7 +580,16 @@
     memcpy (md5sig.tcpm_key, password, keylen);
   sockunion_free (susock);
 #endif /* GNU_LINUX */
-  ret = setsockopt (sock, IPPROTO_TCP, TCP_MD5SIG, &md5sig, sizeof md5sig);
+  if ((ret = setsockopt (sock, IPPROTO_TCP, TCP_MD5SIG, &md5sig, sizeof md5sig)) < 0)
+    {
+      /* ENOENT is harmless.  It is returned when we clear a password for which
+	 one was not previously set. */
+      if (ENOENT == errno)
+	ret = 0;
+      else
+	zlog_err ("sockopt_tcp_signature: setsockopt(%d): %s",
+		  sock, safe_strerror(errno));
+    }
   return ret;
 #else /* HAVE_TCP_MD5SIG */
   return -2;