bgpd: fix using of two pointers for struct thread_master *

bgp is using both bm->master and master pointers interchangebly
for thread manipulation.  Since they are the same thing consolidate
to one pointer.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/bgpd/bgp_network.c b/bgpd/bgp_network.c
index 7059e8a..8621854 100644
--- a/bgpd/bgp_network.c
+++ b/bgpd/bgp_network.c
@@ -207,7 +207,7 @@
       zlog_err ("accept_sock is nevative value %d", accept_sock);
       return -1;
     }
-  listener->thread = thread_add_read (master, bgp_accept, listener, accept_sock);
+  listener->thread = thread_add_read (bm->master, bgp_accept, listener, accept_sock);
 
   /* Accept client connection. */
   bgp_sock = sockunion_accept (accept_sock, &su);
@@ -480,7 +480,7 @@
   listener = XMALLOC (MTYPE_BGP_LISTENER, sizeof(*listener));
   listener->fd = sock;
   memcpy(&listener->su, sa, salen);
-  listener->thread = thread_add_read (master, bgp_accept, listener, sock);
+  listener->thread = thread_add_read (bm->master, bgp_accept, listener, sock);
   listnode_add (bm->listen_sockets, listener);
 
   return 0;