iwlwifi: send ADD_STA before RXON with assoc bit

This patch fixes a bug in association flow. As soon as RXON with assoc bit
is sent, uCode expects to have an entry in its station table that describe
the AP. Receiving a beacon from an HT AP before sending ADD_STA results a
uCode error. This patch sends first the ADD_STA (bcast and bssid) and only
then RXON with assoc bit set

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
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>