Windows: Add Cell name to AFSProcessRequest parameters

Knowing the cell name for the request can be useful to the file
system driver which otherwise does not have access to a conversion
from FileID.CellID to Cell name.

Change-Id: Ia10bae0d9c8bc7824a400ff30268d7ac0b9b2935
Reviewed-on: http://gerrit.openafs.org/9107
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>