bmps mode

[Pontus Fuchs]

Hi Eugene,

I was looking at how wcn36xx uses bmps mode. Currently it's set on 
arrival of BSS_CHANGED_PS. This means we go into bmps mode if power_save 
is enabled (iw dev wlanX power_save on) as soon as the connection has 
been established and we never exit bmps mode.

Shouldn't we move this to IEEE80211_CONF_CHANGE_PS instead? This is 
updated as soon as mac80211 goes in/out of dynamic PS depending on the 
traffic situation? When I tried this I got around twice the throughput.

Cheers,

Pontus