wl1271: hack to disable filters

This is a hack to disable all filters in the join command.  This is based on
Kalle Valo's patch for wl1251.

Cc: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>