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/bgpd.c b/bgpd/bgpd.c
index af8bdb4..3fdd9ff 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -1978,7 +1978,7 @@
   if (name)
     bgp->name = strdup (name);
 
-  THREAD_TIMER_ON (master, bgp->t_startup, bgp_startup_timer_expire,
+  THREAD_TIMER_ON (bm->master, bgp->t_startup, bgp_startup_timer_expire,
                    bgp, bgp->restart_time);
 
   return bgp;
@@ -5421,7 +5421,7 @@
   bgp_vty_init ();
 
   /* Init zebra. */
-  bgp_zebra_init (master);
+  bgp_zebra_init (bm->master);
 
   /* BGP inits. */
   bgp_attr_init ();