net: wireless: bcmdhd: Reduce scan dwell time only in power-save mode

b/17411001

Change-Id: Ia1d34303089e491116b027d2e310de4c4dec9482
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>

Conflicts:

	drivers/net/wireless/bcmdhd/Makefile
	drivers/net/wireless/bcmdhd/dhd.h
	drivers/net/wireless/bcmdhd/dhd_linux.c
	drivers/net/wireless/bcmdhd/wl_cfg80211.c
bcmdhd: add dev_priv struct required by previous commit