mlxsw: spectrum: Bump minimum FW version to xx.2008.2406

The indicated version fixes the following two issues:

- MIRROR_SAMPLER_ACTION.mirror_probability_rate inverted. This has
  implication for per-flow sampling.

- When adjacency is replaced-if-inactive (RATR.opcode=3), bad parameter
  was reported when replacing an active entry. This breaks offload of
  resilient next-hop groups.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>