This patch moves code around and group most of the station
management code into iwl-sta.c

No functional changes (yet)
Signed-off-by: NTomas Winkler <tomas.winkler@intel.com>
Signed-off-by: NReinette Chatre <reinette.chatre@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>