RSNO: Use the RSN Selection element to indicate which variant was used

RSNO: Use the RSN Selection element to indicate which variant was used

This replaces the use of the RSNE Override and RSNE Override 2 elements
with empty payload to indicate which RSNE variant was used.

In addition, this adds stricter validation of the RSNE in
(Re)Association Request frame to allow only the pairwise cipher suites
and AKMs listed in the indicated RSNE variant to be used.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>