Fixes: #19229 Validade interface mode changes

[renatoalmeidaoliveira]

Fixes: #19229 cant unset a device interface vlan mode without an error

• When the user changes the Interface mode, the untagged_vlan and tagged_vlans fields are unset and excluded from the InterfaceForm data.
• Since the form instance is derived from a copy of the concrete object, the untagged_vlan and tagged_vlans remain untouched even when the mode field is modified, leading to a validation error when updating the model.
• The fix ensures that when the form instance's mode field differs from cleaned_data["mode"], these fields are properly removed from the instance when unset, preventing validation errors.