mwifiex: add "ethtool wol" command support

Host sleep wakeup condition is configured using this command.

Supports Wake-on: pumb

For examples:

wake-on any unicast packets:
ethtool -s mlan0 wol u

wake-on multicast/broadcast packet:
ethtool -s mlan0 wol mb

wake-on unicast packets and MAC events:
ethtool -s mlan0 wol pu

wake-on unicast/multicast/broadcast packets and MAC events:
ethtool -s mlan0 wol pmbu

disable all wake-on options:
ethtool -s mlan0 wol d

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>