wl12xx: AP-mode - fix race condition on sta connection

If a sta starts transmitting immediately after authentication, sometimes
the FW deauthenticates it. Fix this by marking the sta "in-connection"
in FW before sending the autentication response.

The "in-connection" entry is automatically removed when connection
succeeds or after a timeout.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>