iproute2: add stp setting

Up unitl now, the iproute2 configurator ignore the bridge object stp
setting. With this patch, if stp is True, the stp_state of the
bridge will be set to 1 (no action for False as the default for
bridge creation is 0).

Change-Id: I5a57aa123d6f5a22c739be4061b35aabea5385fa
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27134
Reviewed-by: Dan Kenigsberg <danken@redhat.com>