net/mlx5: fix default RSS level

net/mlx5: fix default RSS level

Using inner RSS by default for GRE leads to memory corruption as the
extra flow items added for the inner RSS are not counted in the flow
attributes buffer size.

Fixing by enforcing the default RSS level to be outer. This much
simplify the flow engine and more robust.
Future optimization for out of the box RSS can be done on subsequent
commits.

Fixes: d4a405186b73 ("net/mlx5: support tunnel RSS level")

Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>