Flow label is defined as u32 in the in ipv6 flow spec, but
used internally in the flow specs parsing as u8. That was
causing loss of part of flow_label value.

Fixes: 2d1e697e ('IB/mlx5: Add support to match inner packet fields')
Reviewed-by: NMaor Gottlieb <maorg@mellanox.com>
Signed-off-by: NDaria Velikovsky <daria@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>