staging: wfx: with multiple vifs, force PS only if channels differs

staging: wfx: with multiple vifs, force PS only if channels differs

When multiple vif are in use (the only supported configuration is one
station and one AP), the driver force power save flag on station.
This behavior allows the station to leave the station channel and make
its business on AP channel.

However, this has a big impact on station performances (especially since
only legacy PS is supported).

When both vifs use the same channel, it is not necessary to keep this
restriction. This greatly improve station performances.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-42-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>