staging: rtl8723au: rtw_add_beacon(): Construct a full beacon frame for validation

Clean up and correct the beacon frame validation using a full beacon
frame, and pass that to rtw_check_beacon_data23a(). Previous we went
through hoops to construct the frame, minus the ieee80211_3addr header
which just made it more complicated, and resulted in inconsistencies
and bugs.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>