bgpd: Add clear command to force a bestpath recalculation and re-advertisement of a prefix

Add these commands to bgp:

clear ip bgp prefix A.B.C.D/M
clear bgp ipv6 (unicast|multicast) prefix X:X::X:X/M

These two commands forces a bestpath calculation to happen again if
necessary to re-advertise the prefix.

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
diff --git a/bgpd/bgp_table.h b/bgpd/bgp_table.h
index 3b4e6cf..8e963ae 100644
--- a/bgpd/bgp_table.h
+++ b/bgpd/bgp_table.h
@@ -65,6 +65,7 @@
 
   u_char flags;
 #define BGP_NODE_PROCESS_SCHEDULED	(1 << 0)
+#define BGP_NODE_USER_CLEAR             (1 << 1)
 };
 
 /*