ukernel: add morepackets check in listener

ukernel: add morepackets check in listener

Make the listener loop actually check for more packets needed,
like kernel, pthreads and lwp. Only checking for new packets every
20 seconds isn't sufficient on today's networks!

Reviewed-on: http://gerrit.openafs.org/5605
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit eead07418f13cd87a90770f03ea5118c546d8f1a)

Change-Id: I84156d5f1c228e4b3987c17a72ef7c71f0339d4a
Reviewed-on: http://gerrit.openafs.org/5706
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>