cfg80211: allow drivers to support random MAC addresses for scan

Add the necessary feature flags and a scan flag to support using
random MAC addresses for scan while unassociated.

The configuration for this supports an arbitrary MAC address
value and mask, so that any kind of configuration (e.g. fixed
OUI or full 46-bit random) can be requested. Full 46-bit random
is the default when no other configuration is passed.

Also add a small helper function to use the addr/mask correctly.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Git-commit: ad2b26abc157460ca6fac1a53a2bfeade283adfa
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next.git


[dasaris@codeaurora.org: backport to 3.18 excluding the changes in
 nl80211_parse_wowlan_nd]
Change-Id: Id30d201358654c77a99f46500178ebf975d609d5
CRs-Fixed: 1082480
Signed-off-by: Srinivas Dasari <dasaris@codeaurora.org>