keepalive handshake: device_type + keepalive negotiation in UDP/TCP INIT

- Добавлен device_type (1 байт, CLIENT_TYPE_*) в INIT_REQUEST и INIT_RESPONSE
- Добавлен keepalive_interval (2 байта) в INIT_RESPONSE
- STCP handshake расширен с 43 до 46 байт (device_type+keepalive)
- negotiate_keepalive(): оба desktop/server → min, иначе (есть mobile) → max
- keepalive_interval вынесен в UTUN_INSTANCE для использования в handshake
- stcp_client_connect() принимает device_type и keepalive_interval
- peer_device_type/peer_keepalive_interval передаются через stcp_link в ETCP_LINK

src/utun_instance.c

@@ -101,6 +101,7 @@ static int instance_init_common(struct UTUN_INSTANCE* instance, struct UASYNC* u
 
     // Set client type
     instance->client_type = config->global.client_type;
+    instance->keepalive_interval = (uint16_t)(config->global.keepalive_interval > 0 ? config->global.keepalive_interval : 200);
     instance->client_activity = (instance->client_type == CLIENT_TYPE_SERVER) ? CLIENT_ACTIVITY_ACTIVE : CLIENT_ACTIVITY_STANDBY;
     instance->client_activity_timer = NULL;
 
@@ -512,7 +513,7 @@ void utun_instance_destroy(struct UTUN_INSTANCE *instance) {
         if (tc) DEBUG_INFO(DEBUG_CATEGORY_SYS, "[DESTROY] J: closed %d TCP links", tc);
     }
     queue_free(instance->tcp_connections); instance->tcp_connections = NULL;
-    while (instance->tcp_sockets) tcp_socket_remove(instance->tcp_sockets);
+    /* TCP sockets already cleaned in Phase G via etcp_sockets */
     uasync_drain_immediate(instance->ua);
     DEBUG_INFO(DEBUG_CATEGORY_SYS, "[DESTROY] J done — TCP");