mlxsw: spectrum: On port enslavement to a LAG, join upper's bridges

mlxsw: spectrum: On port enslavement to a LAG, join upper's bridges

Currently it never happens that a netdevice that is already a bridge slave
would suddenly become mlxsw upper. The only case where this might be
possible as far as mlxsw is concerned, is with LAG netdevices. But if a LAG
already has an upper, enslaving mlxsw port to that LAG is forbidden. Thus
the only way to install a LAG between a bridge and a mlxsw port is by first
enslaving the port to the LAG, and then enslaving that LAG to a bridge.

However in the following patches, the requirement that ports be only
enslaved to masters without uppers, is going to be relaxed. It will
therefore be necessary to join bridges of LAG uppers. Without this replay,
the mlxsw bridge_port objects are not instantiated, which causes issues
later, as a lot of code relies on their presence.

Therefore in this patch, when the first mlxsw physical netdevice is
enslaved to a LAG, consider bridges upper to the LAG (both the direct
master, if any, and any bridge masters of VLAN uppers), and have the
relevant netdevices join their bridges.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>