Reduce the redundant parameters for addVlan()

Change-Id: I7d94145d833a109929f4d537b83bf0758dc43b91
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/14881
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Tested-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>