openvswitch: Do not send notification if ovs_vport_set_options() failed

There is no need to send a notification if ovs_vport_set_options() failed
and ovs_vport_cmd_set() did not change anything.

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>