Having a bridge-port/team-port setting for a connection that
has a different slave-type makes no sense. Such a configuration
shall be considered invalid, and be fixed by normalization.

Note that there is already a normalization the other way around,
when you omit the "slave-type" but a "master" and one(!) port-type
setting is present, the slave-type is automatically determined
based on the port-type.

The use of this is of course to modify an existing slave connection
to make it a non-slave. Then the invalid port settings should be
automatically removed.

Previously, ifcfg-rh writer would write the "BRIDGING_OPTS" setting
without a "BRIDGE". The reader would then (correctly) ignore the
bridge-port. Avoid that altogehter, by requiring the connection to
strictly verify.