This implements the behavior described in IEEE Std 802.11-2016,
12.4.8.6.6 (Protocol instance behavior - Accepted state) to silently
discard received Confirm message in the Accepted state if the new
message does not use an incremented send-confirm value or if the special
2^16-1 value is used. This avoids unnecessary processing of
retransmitted Confirm messages.
Signed-off-by: Jouni Malinen <j@w1.fi>