mwifiex: skip sending GT_REKEY_OFFLOAD_CFG if firmware has no support

If firmware does not support embedded supplicant, then it in turn
will not support GT rekey offloading. If this is the case, then
driver must not advertise WOWLAN flags related to GTK rekey and
it must also skip sending the GT_REKEY_OFFLOAD_CFG command.

Signed-off-by: Shrenik Shikhare <shrenik@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>