vm/systemd: disable scatter-gather only in ProxyVM

NetVM sometimes doesn't have eth0, eg UsbVM.

vm-systemd/network-proxy-setup.sh

@@ -11,4 +11,5 @@ if [ "x$network" != "x" ]; then
     echo "NS2=$secondary_dns" >> /var/run/qubes/qubes_ns
     /usr/lib/qubes/qubes_setup_dnat_to_ns
     echo "1" > /proc/sys/net/ipv4/ip_forward
+    /sbin/ethtool -K eth0 sg off
 fi

vm-systemd/qubes-network.service

@@ -7,7 +7,6 @@ Before=network.target
 [Service]
 Type=oneshot
 RemainAfterExit=yes
-ExecStartPre=/sbin/ethtool -K eth0 sg off
 ExecStart=/usr/lib/qubes/init/network-proxy-setup.sh
 StandardOutput=syslog