On my Chromebook (Linux 4.19.44 in a VM) and on an AWS EC2
machine, select() was sometimes returning EINTR. This is
harmless and just means you should try again. So let's try
again.
This eliminates a problem where the tunnel fails to come up
correctly and the program needs to be restarted.
Signed-off-by: Avery Pennarun <apenwarr@gmail.com>