use virtio for better network performance

dev-utils/fai-kvm

@@ -129,7 +129,7 @@ fi
 mac=$macprefix:$hex
 
 if [ $usernet = 1 ]; then
-    net=""
+    net="-net nic,name=eth0,model=virtio -net user,name=eth0"
 else
     net="-net nic,macaddr=$mac,model=virtio -net tap,ifname=tap$user,script=no,downscript=no"
 fi