net: Support filtering interfaces on no master

Currently there's support for filtering neighbours/links for interfaces
which have a specific master device (using the IFLA_MASTER/NDA_MASTER
attributes).

This patch adds support for filtering interfaces/neighbours dump for
interfaces that *don't* have a master.
Signed-off-by: Lahav Schlesinger <lschlesinger@drivenets.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20210810090658.2778960-1-lschlesinger@drivenets.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/neighbour.c

@@ -2528,6 +2528,13 @@ static bool neigh_master_filtered(struct net_device *dev, int master_idx)
 		return false;
 
 	master = dev ? netdev_master_upper_dev_get(dev) : NULL;
+
+	/* 0 is already used to denote NDA_MASTER wasn't passed, therefore need another
+	 * invalid value for ifindex to denote "no master".
+	 */
+	if (master_idx == -1)
+		return !!master;
+
 	if (!master || master->ifindex != master_idx)
 		return true;
 

net/core/rtnetlink.c

@@ -1959,6 +1959,13 @@ static bool link_master_filtered(struct net_device *dev, int master_idx)
 		return false;
 
 	master = netdev_master_upper_dev_get(dev);
+
+	/* 0 is already used to denote IFLA_MASTER wasn't passed, therefore need
+	 * another invalid value for ifindex to denote "no master".
+	 */
+	if (master_idx == -1)
+		return !!master;
+
 	if (!master || master->ifindex != master_idx)
 		return true;