fix auto_socket: handle_nl_link silently skipped on if_indextoname failure for deleted interfaces

When ip link del removes an interface, the kernel sends RTM_DELLINK after the interface is unregistered from the name table.
if_indextoname fails and handle_nl_link silently returned without calling remove_iface_sockets,
causing old ETCP sockets to accumulate indefinitely.

Fix: fall through to remove_iface_sockets(ifindex) even when if_indextoname fails.

Test: added diagnostics (diag_dump_state, per-category debug levels to file) to verify socket/links cleanup.

src/transport_layer/auto_socket.c

@@ -932,7 +932,12 @@ static void handle_nl_addr(struct AUTO_SOCKET* as, struct ifaddrmsg* ifa, int ms
  *   - UP (новый или поднялся) → запускаем reconcile */
 static void handle_nl_link(struct AUTO_SOCKET* as, struct ifinfomsg* ifi, int msg_type) {
     char ifname[IFNAMSIZ];
-    if (!if_indextoname(ifi->ifi_index, ifname)) return;
+    if (!if_indextoname(ifi->ifi_index, ifname)) {
+        DEBUG_WARN(DEBUG_CATEGORY_AS, "[as] handle_nl_link: if_indextoname(%u) failed, msg=%d — removing by index",
+                   ifi->ifi_index, msg_type);
+        remove_iface_sockets(as, ifi->ifi_index);
+        return;
+    }
     if (ifi->ifi_flags & IFF_LOOPBACK) return;
 
     int is_up = (ifi->ifi_flags & IFF_UP) != 0;