nl80211: add packet offset information for wowlan pattern

If user knows the location of a wowlan pattern to be matched in
Rx packet, he can provide an offset with the pattern. This will
help drivers to ignore initial bytes and match the pattern
efficiently.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
[refactor pattern sending]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>