[PATCH] iwlwifi: clear station table in rxon unconditionally

This patch clears stations table for every rxon command.
It removes iwl_rxon_add_station function in 3945.

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