ripd: set IP TOS for control socket

* ripd.c: (rip_create_socket) RIP packets should go out with Type Of Service
  (DSCP) set to Internet control (like OSPF and BGP).
diff --git a/ripd/ripd.c b/ripd/ripd.c
index c865ace..2d5a856 100644
--- a/ripd/ripd.c
+++ b/ripd/ripd.c
@@ -1372,6 +1372,9 @@
 #ifdef RIP_RECVMSG
   setsockopt_pktinfo (sock);
 #endif /* RIP_RECVMSG */
+#ifdef IPTOS_PREC_INTERNETCONTROL
+  setsockopt_ipv4_tos (sock, IPTOS_PREC_INTERNETCONTROL);
+#endif
 
   if (ripd_privs.change (ZPRIVS_RAISE))
       zlog_err ("rip_create_socket: could not raise privs");