A warning message should appear when entering a MAC adress already belonging to another user.

[Gadac1]

This would allow us to track transferred router between tenants.
The message should display to whom the MAC already belongs.

Bisous,
Gadac

[Letiste]

We could also add a "transfer MAC" option, like in re2o with the rooms.

[Letiste]

If MAC exists already, replace it by default and display a undo message after creation (same for the room)