nl80211: add support for BSS coloring

This patch adds support for BSS color collisions to the wireless subsystem.
Add the required functionality to nl80211 that will notify about color
collisions, triggering the color change and notifying when it is completed.

Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: John Crispin <john@phrozen.org>
Link: https://lore.kernel.org/r/500b3582aec8fe2c42ef46f3117b148cb7cbceb5.1625247619.git.lorenzo@kernel.org
[remove unnecessary NULL initialisation]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>