net/mlx5e: Remove wrong and superfluous tc pedit header type check

With recent introduction of flow_rule infrastructure drivers no longer
directly include action headers, so it is no longer possible to use
constants defined in them. Instead, one of flow_rule patches substituted
pedit action header constant with hardcoded value '2' in mlx5
set_pedit_val() function conditional which verifies that header type is in
range of values allowed by pedit action. That conditional is now both
wrong (hardcoded value is '2' but __PEDIT_HDR_TYPE_MAX is 6 in current
version) and superfluous (pedit action already verifies that header type is
in allowed range during init). Remove the described check from mlx5 code.

Fixes: 73867881

 ("drivers: net: use flow action infrastructure")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Dmytro Linkin <dmitrolin@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>