Use netvm_gw_ip instead of netvm_ip

They are usually identical, but this is not guaranteed.

network/vif-qubes-nat.sh

@@ -95,7 +95,7 @@ if test "$command" == online; then
     fi
 
     netns ip neighbour add to "$appvm_ip" dev "$netns_appvm_if" lladdr "$mac" nud permanent
-    netns ip neighbour add to "$netvm_ip" dev "$netns_netvm_if" lladdr "$netvm_mac" nud permanent
+    netns ip neighbour add to "$netvm_gw_ip" dev "$netns_netvm_if" lladdr "$netvm_mac" nud permanent
     netns ip addr add "$netvm_ip" dev "$netns_netvm_if"
     netns ip addr add "$appvm_gw_ip" dev "$netns_appvm_if"