netcardconfig: avoid dns-nameservers leaking into gateway variable

Because we also take care of the dns-nameservers entry in
/etc/network/interfaces, when re-executing netcardconfig we
overload the default gateway variable with *also* the
dns-nameservers entry, which is clearly unwanted.
So avoid leaking the dns-nameservers entry into the
gateway variable (which is presented in the gateway
input dialog) by assigning it its own variable.

sbin/netcardconfig

@@ -442,7 +442,7 @@ configiface() {
         /gateway/{if(found){gateway=$NF}}
         /dns-nameservers/{if(found){dnsnameservers=$NF}}
         END{print address" "netmask" "broadcast" "gateway" "dnsnameservers}' /etc/network/interfaces >"$TMP"
-      read IP NM BC DG <"$TMP"
+      read IP NM BC DG NS <"$TMP"
       rm -f "$TMP"
     fi