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/aspath_test.c b/tests/aspath_test.c
index 83eb9d8..9170455 100644
--- a/tests/aspath_test.c
+++ b/tests/aspath_test.c
@@ -1259,6 +1259,7 @@
   int i = 0;
   bgp_master_init ();
   master = bm->master;
+  bgp_option_set (BGP_OPT_NO_LISTEN);
   bgp_attr_init ();
   
   while (test_segments[i].name)