Extend the MAC address validator to disallow multicast MAC addresses and
add a new optional validator option to require multicast MACs instead of
unicast ones.
Fixes: #5166
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 00e41c3c4977f75e6ca43429dd4c8c2f5cb22419)
1fed9af22c