net: dsa: felix: propagate the LAG offload ops towards the ocelot lib

The ocelot switch has been supporting LAG offload since its initial
commit, however felix could not make use of that, due to lack of a LAG
abstraction in DSA. Now that we have that, let's forward DSA's calls
towards the ocelot library, who will deal with setting up the bonding.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 8fe6832e)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
[Xulin: Original patch taken from
https://github.com/vladimiroltean/linux/commits/felix-dsa-tag-vlan-stable

]
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>