Basic implementation of TCP over XDP for Knot server

including connection handling for kxdpgun in TCP mode.

The implementation is not perfect!! But the interface with other Knot parts is stable.

src/knot/conf/conf.c

@@ -1175,7 +1175,7 @@ size_t conf_xdp_threads_txn(
 	while (val.code == KNOT_EOK) {
 		struct sockaddr_storage addr = conf_addr(&val, NULL);
 		conf_xdp_iface_t iface;
-		int ret = conf_xdp_iface(&addr, false, &iface);
+		int ret = conf_xdp_iface(&addr, &iface);
 		if (ret == KNOT_EOK) {
 			workers += iface.queues;
 		}
@@ -1338,7 +1338,6 @@ conf_remote_t conf_remote_txn(
 
 int conf_xdp_iface(
 	struct sockaddr_storage *addr,
-	bool tcp,
 	conf_xdp_iface_t *iface)
 {
 #ifndef ENABLE_XDP
@@ -1355,14 +1354,12 @@ int conf_xdp_iface(
 		const char *port = strchr(addr_str, '@');
 		if (port != NULL) {
 			iface->name[port - addr_str] = '\0';
-			uint16_t res = 0;
-			int ret = str_to_u16(port + 1, &res);
+			int ret = str_to_u16(port + 1, &iface->port);
 			if (ret != KNOT_EOK) {
 				return ret;
-			} else if (res == 0) {
+			} else if (iface->port == 0) {
 				return KNOT_EINVAL;
 			}
-			iface->port = res;
 		} else {
 			iface->port = 53;
 		}
@@ -1385,10 +1382,6 @@ int conf_xdp_iface(
 	}
 	iface->queues = queues;
 
-	if (tcp) {
-		iface->port |= KNOT_XDP_LISTEN_PORT_TCP;
-	}
-
 	return KNOT_EOK;
 #endif
 }