kernel-netlink: Directly handle Netlink messages if thread pool is empty

During initialization of the plugins the thread pool is not yet
initialized so there is no watcher thread that could handle the queued
Netlink message and the main thread will wait indefinitely for a
response.

Fixes #2199.

src/libcharon/plugins/kernel_netlink/kernel_netlink_shared.c

@@ -333,7 +333,8 @@ static status_t send_once(private_netlink_socket_t *this, struct nlmsghdr *in,
 	while (!entry->complete)
 	{
 		if (this->parallel &&
-			lib->watcher->get_state(lib->watcher) != WATCHER_STOPPED)
+			lib->watcher->get_state(lib->watcher) != WATCHER_STOPPED &&
+			lib->processor->get_total_threads(lib->processor))
 		{
 			if (this->timeout)
 			{