net: wireless: bcmdhd: Reduce scan dwell time to reduce power

Scan dwell time is reduced for 40/80 to 20/40 (normal)
and 20/30 (power-save). Scan quality reduction is ~ 20%.

b/17485849

Change-Id: I00d6e5ef83df8b075b48736daaa6e814dd09054a
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com> (reverted from commit 4c00434b2e556d24b7ec293b4cad95d45f081553)
bcmdhd: add dev_priv struct required by previous commit (reverted from commit ef05e8f0a2520289e75a6db41c5528cd8a353ff2)
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

Conflicts:

	drivers/net/wireless/bcmdhd/Makefile (reverted from commit b9470192967fdcd0f66d7bedfc5bd452c1b945f5)