Flush output buffers in the tap reader thread on Windows.

This is basically a port of commit 50fcfea1 to 1.1.

src/mingw/device.c

@@ -80,6 +80,7 @@ static DWORD WINAPI tapreader(void *bla) {
 		packet.len = len;
 		packet.priority = 0;
 		route(myself, &packet);
+		event_flush_output();
 		LeaveCriticalSection(&mutex);
 	}
 }