socket_monitor: extract socket monitoring from etcp_connections, add per-instance context

- New files: transport_layer/socket_monitor.c/h — socket state monitoring with per-instance ctx
- etcp_api: expose get_latency/1s_pkt_count measuring, add etcp_hashrnd for tests
- utun_instance: store socket_monitor per instance, add is_socket_ok check
- topo_node: detect IPv4 addresses with port from listening sockets
- topo_group: use node_name for display in routes
- Makefile.am: add socket_monitor.c to build

src/utun_instance.c

@@ -19,6 +19,7 @@
 #include "stcp_server.h"
 #include "control_server.h"
 #include "transport_layer/node_conn_direct.h"
+#include "transport_layer/socket_monitor.h"
 
 #include "../lib/u_async.h"
 #include "../lib/debug_config.h"
@@ -218,6 +219,8 @@ static int instance_init_common(struct UTUN_INSTANCE* instance, struct UASYNC* u
         instance->topo_groups = NULL;
     }
 
+    socket_monitor_init(instance);
+
     // conn_mgr initialized inside topo_group_create (via topo_groups_init)
     
     // Initialize firewall
@@ -430,6 +433,8 @@ void utun_instance_destroy(struct UTUN_INSTANCE *instance) {
     }
     instance->config_conn_handles = NULL;
 
+    socket_monitor_destroy(instance);
+
     // Cleanup BGP module BEFORE sockets (needs live conn_mgr for recovery cleanup)
     if (instance->topo_groups) {
         DEBUG_INFO(DEBUG_CATEGORY_BGP, "Destroying BGP module");