bcmdhd: filter multicast packages while in suspend

In some crowded WLANs, with a lot of multicast packages circulating,
the device would not enter deep sleep.
This will allow the device to enter deep sleep.

Change-Id: Id25f1c0da163c822d5a6b7cc60f183f9bd9ae7fa
Signed-off-by: zwliew <zhaoweiliew@gmail.com>