dos: Pass transport name on new client connection

For a bridge configured with a pluggable transport, the transport name is
used, with the IP address, for the GeoIP client cache entry.

However, the DoS subsystem was not aware of it and always passing NULL when
doing a lookup into the GeoIP cache.

This resulted in bridges with a PT are never able to apply DoS defenses for
newly created connections.

Fixes #33491

Signed-off-by: David Goulet <dgoulet@torproject.org>