wl1251: add powersave exit logic for transfers

Exiting powersave during transfers improves data rates.
Now that mac80211 no longer manages PS, the driver has to do it itself.

diff --cc drivers/net/wireless/wl1251/main.c
Simple merge

diff --cc drivers/net/wireless/wl1251/rx.c
Simple merge

diff --cc drivers/net/wireless/wl1251/sdio.c
Simple merge

diff --cc drivers/net/wireless/wl1251/tx.c
Simple merge

diff --cc drivers/net/wireless/wl1251/wl1251.h
Simple merge