iwlwifi: replacing wording restricted to nic access in iwl-io

This patch replaces wording 'restricted' with more appropriate 'nic access'
NIC access is grabbed to prevent NIC entering power save mode
General cleanup of iwl-io.h

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>