bgpd: Fix crash reported by NetDEF CI

This patch is part of the previously submitted
 patch set on VPN and Encap SAFIs.  It fixes
 an issue identified by NetDEF CI.

 Ensure temp stack structures are initialized
 Add protection against double frees / post
 free access to bgp_attr_flush

    Signed-off-by: Lou Berger <lberger@labn.net>
diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index 2728b10..c364372 100644
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -2121,6 +2121,9 @@
   const char *reason;
   char buf[SU_ADDRSTRLEN];
 
+  memset (&new_attr, 0, sizeof(struct attr));
+  memset (&new_extra, 0, sizeof(struct attr_extra));
+
   bgp = peer->bgp;
   rn = bgp_afi_node_get (bgp->rib[afi][safi], afi, safi, p, prd);