Windows: Update Bulk I/O Descriptor

Update the cm_bulkIO_t and associated functions such that
the 'reserved' field is no longer a boolean indicated whether
or not buffers have been reserved but instead becomes a count
of the number of buffers that have been reserved.

buf_TryReserveBuffers is modified to return an afs_uint64
count of the number of buffers reserved instead of a boolean.

cm_SetupStoreBIOD, cm_SetupFetchBIOD, and cm_ReleaseBIOD altered
to store the reserved buffer count and use it when freeing the
BIOD.

Prior to this change it was not possible to reserve a count other
than the number of buffers it takes to store one chunkSize of data.

Reviewed-on: http://gerrit.openafs.org/8951
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 23fa416581568c2c58c6f2739139b9486ba8fa10)

Change-Id: I38aba9f0af1ff550ee3993f99cf598be1faa7741
Reviewed-on: http://gerrit.openafs.org/9015
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: rename 'rbytes' to 'rxbytes' for clarity

Throughout cm_dcache.c, the various 'rbytes' represents the number
of bytes to be read from the next rx_Read or rx_Readv call.
Rename the variable to 'rxbytes' to improve clarity.

Reviewed-on: http://gerrit.openafs.org/8952
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit bf4cda8a5551719a005e4f927dfd1fb25dc2c219)

Change-Id: Iab90767ef8c10fe8d2614d4deafcb12dd1318062
Reviewed-on: http://gerrit.openafs.org/9016
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>