Empty IE buffer means that the new association is not supposed to
include extra IEs. Make sure any previously configured (Re)Association
Request frame IEs get cleared in such a case. This is based on a patch
from Shuibing.

Cc: Dai Shuibing <shuibing@qca.qualcomm.com>
Signed-off-by: NJouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: NKalle Valo <kvalo@qca.qualcomm.com>