bsd: Fix set_key() sequence number endian issue

bsd: Fix set_key() sequence number endian issue

In set_key handler, the seq[8] is in little endian order defined by
WPA. BSD kernel uses a u_int64_t value ik_keyrsc to represent it
internally. The kernel expects the native endian order for the value.
Thus, we need to detect the endian order and swap bytes when
necessary.