[feature] Enforce MAC address format for called_station_id and calling_station_id

[pandafy]

The MAC address format stored in called_station_id and calling_station_id can vary depending on the NAS. This causes inconsistency in values of these fields.

We can provide a setting which allows user to specify a format.

Using the clean method at model level, the code shall update the field values according to the user specified format.

[Nexusrex18]

Hi @pandafy I implemented an approach in which created a check for MAC addresses. Since different routers send MAC addresses in different styles (some use dashes -, some use colons :, some use dots .), our database was getting messy.
Fix:
Modified the system(RadiusAccounting model) will save MAC addresses to the database automatically in this way:
-> Intercepts the incoming address
-> Translates it into a single, standard format
-> Saves the clean version

What do you think of this approach ?