tests: BGP unit tests to set BGP_OPT_NO_LISTEN so they can run

BGP tests had been broken by auto-creation of listen socket. This allows
them to run at least, though at least 1 test seems to have other breakage,
aspath_test.
diff --git a/tests/bgp_mp_attr_test.c b/tests/bgp_mp_attr_test.c
index 1a48f4b..f086740 100644
--- a/tests/bgp_mp_attr_test.c
+++ b/tests/bgp_mp_attr_test.c
@@ -515,6 +515,7 @@
   
   master = thread_master_create ();
   bgp_master_init ();
+  bgp_option_set (BGP_OPT_NO_LISTEN);
   
   if (fileno (stdout) >= 0) 
     tty = isatty (fileno (stdout));