staging: wfx: introduce wfx_set_default_unicast_key()

Currently code handle WEP keys manually. It is far easier to use
the set_default_unicast_key() callback provided by mac80211.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200420160311.57323-11-Jerome.Pouiller@silabs.com


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