[cleanup] convert bzero() deprecated by POSIX to memset()

autoscan 2.62 complains about bzero(), so a good fix
nowadays is to just replace it.
diff --git a/zebra/irdp_interface.c b/zebra/irdp_interface.c
index b3a838b..d982c23 100644
--- a/zebra/irdp_interface.c
+++ b/zebra/irdp_interface.c
@@ -101,7 +101,7 @@
 
   zi = ifp->info;
 
-  bzero (&m, sizeof (m));
+  memset (&m, 0, sizeof (m));
   m.imr_multiaddr.s_addr = htonl (group);
   p = irdp_get_prefix(ifp);