stcp: multiple servers support via linked list in UTUN_INSTANCE

- Replace instance->stcp_server (single pointer) with stcp_servers linked list
- Add stcp_server_list_add/destroy_all/count API in stcp_link.h/c
- Fix port extraction for both AF_INET and AF_INET6 in init_sockets
- Filter out 0.0.0.0 and [::] addresses in chat_profile.c TCP address sync
- Add type=public to servers in node_config.cpp saveFull()

tools/chatgui/transport/node_config.cpp

@@ -328,7 +328,8 @@ bool NodeConfig::saveFull() {
 
     for (auto& srv : m_servers) {
         out << "[server:" << srv.first << "]\n";
-        out << "addr=" << srv.second << "\n\n";
+        out << "addr=" << srv.second << "\n";
+        out << "type=public\n\n";
     }
 
     for (auto& cli : m_clients) {