android: Mitigate race condition on reauthentication

If the TUN device gets recreated while another thread in handle_plain()
has not yet called select(2) but already stored the file descriptor of the
old TUN device in its FD set, select() will fail with EBADF.

Fixes #301.

src/frontends/android/jni/libandroidbridge/backend/android_service.c

@@ -167,6 +167,10 @@ static job_requeue_t handle_plain(private_android_service_t *this)
 
 	if (len < 0)
 	{
+		if (errno == EBADF)
+		{	/* the TUN device got closed just before calling select(), retry */
+			return JOB_REQUEUE_FAIR;
+		}
 		DBG1(DBG_DMN, "select on TUN device failed: %s", strerror(errno));
 		return JOB_REQUEUE_NONE;
 	}