viced: Rationalise FS_STATS_DETAILED logging

viced: Rationalise FS_STATS_DETAILED logging

Every RPC handler in the fileserver contained a copy of an identical
code block to handle starting, stopping, and recording detailed logging
statistics. Replace all of this with a structure and 4 helper functions,
which will make maintenance much easier.

Change-Id: Ie2b0fa13fcc3e261ba435f1560e7ab5adf477afb
Reviewed-on: http://gerrit.openafs.org/4765
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>