mwifiex: Add missing endian conversion.

commit 83e612f632c3897be29ef02e0472f6d63e258378 upstream.

Both type and pkt_len variables are in host endian and these should be in
Little Endian in the payload.

Signed-off-by: Tomasz Moń <desowin@gmail.com>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>