ptserver: increase the max lwp threads

Increase the maximum LWP threads allowed from 16 to 64. Increasing the number
of LWP threads can reduce the number of calls waiting for threads.

Change-Id: I66f53c0fbb2db66c94b9982e3ee6b3b1f89a0f01
Reviewed-on: http://gerrit.openafs.org/9707
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: Derrick Brashear <shadow@your-file-system.com>