mlxsw: spectrum: Set port's mode according to FID mappings

We currently transition the port to "Virtual mode" upon the creation of
its first VLAN upper, as we need to classify incoming packets to a FID
using {Port, VID} and not only the VID.

However, it's more appropriate to transition the port to this mode when
the {Port, VID} are actually mapped to a FID. Either during the
enslavement of the VLAN upper to a VLAN-unaware bridge or the
configuration of a router port.

Do this change now in preparation for the introduction of the FID core,
where this operation will be encapsulated.

To prevent regressions, this patch also explicitly configures an OVS
slave to "Virtual mode". Otherwise, a packet that didn't hit an ACL rule
could be classified to an existing FID based on a global VID-to-FID
mapping, thus not incurring a FID mis-classification, which would
otherwise trap the packet to the CPU to be processed by the OVS daemon.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>