networks: Fix spacing of helper text in "Create" dialog

The "IP configuration" FormGroup had the isStack property set, which
in turn would change the top margin of FormHelperText inside that
FormGroup from 4 pixels to -4 pixels.

The isStack property does not seem to have any other effect, so let's
remove it.

Fixes: #1164

Author: mvollmer

src/components/networks/createNetworkDialog.tsx

@@ -258,7 +258,7 @@ const IpRow = ({
     validationFailed: ValidationFailed,
 }) => {
     return (
-        <FormGroup fieldId='create-network-ip-configuration' label={_("IP configuration")} isStack>
+        <FormGroup fieldId='create-network-ip-configuration' label={_("IP configuration")}>
             <FormSelect id='create-network-ip-configuration'
                         value={dialogValues.ip}
                         onChange={(_event, value) => onValueChanged('ip', value)}>