Although the kek_len should have already been validated before the
function is called, update wlan_hdd_save_gtk_offload_params() to limit
kek_len to the maximum allowed value before using it to copy the kek.
Change-Id: I0676521171343c6fe58afcdc31477f555598c490
CRs-Fixed: 2140033
e1f2b0e66a