bgpd: Fix small memory leak in str2prefix_rd

str2prefix_rd has a memory leak.  This commit fixes that issue

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/bgpd/bgp_mplsvpn.c b/bgpd/bgp_mplsvpn.c
index cf4ab6f..8a1ed70 100644
--- a/bgpd/bgp_mplsvpn.c
+++ b/bgpd/bgp_mplsvpn.c
@@ -220,6 +220,7 @@
     }
   memcpy (prd->val, s->data, 8);
 
+  XFREE(MTYPE_TMP, half);
   return 1;
 }