core dom0 rpm: restart qubes_netvm only when using netvm in Dom0

If we use a separate netvm, then core update in Dom0 doesn't really change the networking,
worse, if we restarted netvm it would get another XID, which would break our DispVM savefile.

One day we should fix it!

rpm_spec/core-dom0.spec

@@ -173,7 +173,11 @@ for i in /usr/share/qubes/icons/*.png ; do
 done
 
 /etc/init.d/qubes_core start
-/etc/init.d/qubes_netvm start
+
+NETVM=$(qvm-get-default-netvm)
+if [ $NETVM = "dom0" ] ; then
+    /etc/init.d/qubes_netvm start
+fi
 
 
 %clean
@@ -186,7 +190,11 @@ fi
 
 if [ "$1" -gt 1 ] ; then
     # upgrading already installed package...
+    NETVM=$(qvm-get-default-netvm)
+    if [ $NETVM = "dom0" ] ; then
         /etc/init.d/qubes_netvm stop
+    fi
+
     /etc/init.d/qubes_core stop
 fi