net: dsa: Add helper to resolve bridge port from DSA port

In order for a driver to be able to query a bridge for information
about itself, e.g. reading out port flags, it has to use a netdev that
is known to the bridge. In the simple case, that is just the netdev
representing the port, e.g. swp0 or swp1 in this example:

   br0
   / \
swp0 swp1

But in the case of an offloaded lag, this will be the bond or team
interface, e.g. bond0 in this example:

     br0
     /
  bond0
   / \
swp0 swp1

Add a helper that hides some of this complexity from the
drivers. Then, redefine dsa_port_offloads_bridge_port using the helper
to avoid double accounting of the set of possible offloaded uppers.

Signed-off-by: Tobias Waldekranz <[email protected]>
Reviewed-by: Vladimir Oltean <[email protected]>
Reviewed-by: Florian Fainelli <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions