network: run setup-ip only on xen frontend interfaces

Fixes QubesOS/qubes-issues#1882

network/udev-qubes-network.rules

@@ -1,2 +1,2 @@
 
-SUBSYSTEMS=="xen", KERNEL=="eth*", ACTION=="add", RUN+="/usr/lib/qubes/setup-ip"
+SUBSYSTEMS=="xen", KERNEL=="eth*", ACTION=="add", ENV{ID_NET_DRIVER}=="vif", RUN+="/usr/lib/qubes/setup-ip"