mlxsw: spectrum_router: Demote tunnels on VRF migration

The mlxsw driver currently doesn't offload GRE tunnels if they have the
same local address and use the same underlay VRF. When such a situation
arises, the tunnels in conflict are demoted to slow path.

However, the current code only verifies this condition on tunnel
creation and tunnel change, not when a tunnel is moved to a different
VRF. When the tunnel has no bound device, underlay and overlay are the
same. Thus moving a tunnel moves the underlay as well, and that can
cause local address conflict.

So modify mlxsw_sp_netdevice_ipip_ol_vrf_event() to check if there are
any conflicting tunnels, and demote them if yes.

Fixes: af641713

 ("mlxsw: spectrum_router: Onload conflicting tunnels")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>