net: wireless: bcmdhd change the DTIM skip policy

1) Bug: 22808829
2) Device will wake up at every another DTIM on scree off.
   However, the extended DTIM skip period will not be bigger than 400ms
   So, if the DTIM interval is 300ms, device will still wake up at every DTIM
   on screen off becaues of 400ms limitation.
Signed-off-by: Ecco Park <eccopark@broadcom.com>

Change-Id: I8ad0d453b756797a3c9f1c575c65b303842355f3