mlxsw: spectrum_switchdev: Have VXLAN device take reference on FID

Up until now only local ports and the router port (which is also a local
port) took a reference on the corresponding FID (Filtering Identifier)
when joining a bridge. For example:

        192.0.2.1/24
            br0
             |
      +------+------+
      |             |
     swp1        vxlan0

In this case the reference count of the FID will be '2'. Since the VXLAN
device does not take a reference on the FID, whenever a local port joins
the bridge it needs to check if a VXLAN device is already enslaved. If
the VXLAN device should be mapped to the FID in question, then the VXLAN
device's VNI is set on the FID.

Beside the fact that this scheme special-cases the VXLAN device, it also
creates an unnecessary dependency between the routing and bridge code:

1. [R] IP address is added on 'br0', which prompts the creation of a RIF
   and a backing FID
2. [B] VNI is enabled on backing FID
3. [R] Host route corresponding to VXLAN device's source address is
   promoted to perform NVE decapsulation

[R] - Routing code
[B] - Bridge code

This back and forth dependency will become problematic when a lock is
added in the routing code instead of relying on RTNL, as it will result
in an AA deadlock.

Instead, have the VXLAN device take a reference on the FID just like all
the other netdev members of the bridge. In order to correctly handle the
case where VXLAN devices are already enslaved to the bridge when it is
offloaded, walk the bridge's slaves and replay the configuration.

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