bgpd: mark route nodes scheduled into work queue

The flag bit BGP_NODE_PROCESS_SCHEDULED is checked but never set.
This causes route node to be scheduled multiple times under load.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index 6155bc1..06bd599 100644
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -1695,6 +1695,7 @@
         break;
     }
   
+  SET_FLAG (rn->flags, BGP_NODE_PROCESS_SCHEDULED);
   return;
 }