Comment 1 for bug 1843428

I need to dig into where this is actually handled, but case-insensitive search work here:
(devstack master)
$ openstack port list --mac-address FA:16:3e:67:9b:4F -f value -c mac_address
fa:16:3e:67:9b:4f
(RHOSP 13, so queens release)
$ openstack port list --mac-address FA:16:3e:b4:A7:c3 -f value -c id
f9c080ef-be07-4ff4-b3ee-d866b0029a43
Sorry I do not have a vanilla queens env around to confirm that last bit

So this was probably fixed at some point and you may just be missing a backport