iwlwifi: mvm: open BA session only when sta is authorized

Currently, a BA session is opened when the tx traffic exceeds
10 frames per second. As a result of inter-op problems with some
APs, add a condition to open BA session only when station is
already authorized.

Fixes: 482e4844 ("iwlwifi: mvm: change open and close criteria of a BA session")
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>