staging: wfx: add missing PROBE_RESP_OFFLOAD feature

Some userspace tools (hostapd) rely on probe_resp_offload fields for
certain features.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-4-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>