staging: rtl8723au: issue_auth(): Convert to using struct ieee80211_mgmt

This reduces the dependency of rtw_set_fixed_ie23a() which is
scheduled to go away.

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