Sorry, but the only way is to shutdown and restart the amule daemon.
I have noticed that with amuled 2.1.2 on Mandrake Kad usually lives longer than all previous versions, but still it's a bit hit and miss. I have had 6 days of uptime before it disconnected, but also within 14 hours.
I guess it's about UDP on the both the Linux and the router, but it's hard to tell.