mlxsw: spectrum_nve: Replace error code with EINVAL

Adding a VLAN on a port can trigger the offload of a VXLAN tunnel which
is already a member in the VLAN. In case the configuration of the VXLAN
is not supported, the driver would return -EOPNOTSUPP.

This is problematic since bridge code does not interpret this as error,
but rather that it should try to setup the VLAN using the 8021q driver
instead of switchdev.

Fixes: d70e42b2 ("mlxsw: spectrum: Enable VxLAN enslavement to VLAN-aware bridges")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>