Check for capability CAP_NET_ADMIN before allowing changing switch device configuration

Signed-off-by: Elliott Mitchell <ehem+openwrt@m5p.com>

--- a/target/linux/generic/files/drivers/net/phy/swconfig.c
+++ b/target/linux/generic/files/drivers/net/phy/swconfig.c
@@ -635,6 +635,10 @@ swconfig_set_attr(struct sk_buff *skb, struct genl_info *info)
 	struct switch_val val;
 	int err = -EINVAL;
 
+	/* check for appropriate permission before allowing setting changes */
+	if(!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	dev = swconfig_get_dev(info);
 	if (!dev)
 		return -EINVAL;