Remove network.target from "After" dependencies of openvswitch-switch.service (Closes: #924562)

networking.service specifies Before=network.target. So
openvswitch-switch.service should run before (via networking.service)
and after network.target, which is an unsolvable loop dependency.

Thanks: Benjamin Drung

debian/openvswitch-switch.service

 [Unit]
 Description=Open vSwitch
-After=network.target openvswitch-nonetwork.service
+After=openvswitch-nonetwork.service
 Requires=openvswitch-nonetwork.service
 Before=networking.service