FST: Fix byte order of couple of fields on big endian hosts

FST: Fix byte order of couple of fields on big endian hosts

Couple of fsts_id and llt fields were not properly swapped from host
byte order to little endian byte order used in the frames. Fix this and
use the le32 type to make this more consistent and verifiable with
sparse.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>