etcp_connect + BGP_READY callbacks + router reconnect test

- etcp_connect.c: async connect API with EARLY/LATE/BGP_READY callbacks
- etcp_connect.h: declaration (via etcp_api.h)
- connect_deliver: fix to preserve unfired callback nodes
- etcp_set_routing_exchange_state: fires bgp_ready_cbk on TABLE_COMPLETE
- route_bgp: TABLE_COMPLETE handler + route_bgp_send_table_complete
- etcp.c: connections_count tracking, cleanup on close
- test_etcp_router_reconnect: a-b-c topology with b restart (etcp_connect)
- test_etcp_connect: unit tests for async connect API
- etcp_router: inflight/retrans/close improvements
- Various proxy/NAT/router cleanups

lib/debug_config.c

@@ -128,6 +128,7 @@ static const struct {
     {"keepalive", DEBUG_CATEGORY_KEEPALIVE},
     {"etcp_route", DEBUG_CATEGORY_ETCPROUTE},
     {"bbr", DEBUG_CATEGORY_BBR},
+    {"etcp_dump", DEBUG_CATEGORY_ETCP_DUMP},
     {"all", DEBUG_CATEGORY_ALL},
     {NULL, DEBUG_CATEGORY_NONE}
 };