The IWL_MAX_CMD_TFDS name for this constant is wrong, the
constant really indicates how many TBs we can use in the
driver for a single command TFD, rename the constant and
also add a comment explaining it.
Reviewed-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>