iwlagn: move iwl_stop / wake_queue to the upper layer

Add a wrapper in the upper layer to call the mac80211's function.
This allows not to have the transport layer call mac80211 directly.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>