iwlwifi-2.6: Cleans up set_key flow

This patch cleans up the set_key flow. Rxon with hw encryption bit set is
not sent upon each call to set_key. Separation is made between global key
(WEP) and dynamic key (TKIP + CCMP and WEP in some cases).

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