mlxsw: spectrum_fid: Implement missing operations for rFID and dummy FID

rFID and dummy FID do not support FID->VNI mapping. Currently, these
families do not implement the vni_{set, clear}() operations. Instead, there
is a check if these functions are implemented.

Similarly, 'SFMR.nve_tunnel_flood_ptr' is not relevant for rFID and dummy
FID, therefore, these families do not implement
nve_flood_index_{set, clear}().

Align the behavior to other unsupported operations, implement the functions
and just return an error or warn. Then, checks like '!ops->vni_set' can be
removed.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>