connection: improve kdbus_cmd_conn_update() connection type checks

connection: improve kdbus_cmd_conn_update() connection type checks

Do another round of connection type checks inside the KDBUS_ITEM
iterator.

We need this since we do not want to allow ordinary connections to
update policy entries that belong to another policy holder connection.

We also do it for the attach flags since only ordinary connections are
interessted in it.

And update a kdbus_policy_set() call to only pass a one name per
policy-holding connection

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>