bgpd: crash if attributes alone consume > 4096 bytes

This patch fixes a crash if attributes on a patch consume
more than 4096 bytes.

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index 3f6161c..40da02e 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -278,6 +278,8 @@
   BGP_PEER_CONFED,
 } bgp_peer_sort_t;
 
+#define BGP_MAX_PACKET_SIZE_OVERFLOW          1024
+
 /* BGP neighbor structure. */
 struct peer
 {