l3mdev: add function to retreive upper master

Existing functions to retreive the l3mdev of a device did not walk the
master chain to find the upper master. This patch adds a function to
find the l3mdev, even indirect through e.g. a bridge:

+----------+
|          |
| vrf-blue |
|          |
+----+-----+
     |
     |
+----+-----+
|          |
| br-blue  |
|          |
+----+-----+
     |
     |
+----+-----+
|          |
|   eth0   |
|          |
+----------+

This will properly resolve the l3mdev of eth0 to vrf-blue.

Signed-off-by: Alexis Bauvin <[email protected]>
Reviewed-by: Amine Kherbouche <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Tested-by: Amine Kherbouche <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions