net/mlx5: E-switch, Set to legacy mode if failed to change switchdev mode

No need to rollback to the other mode because probably will fail
again. Just set to legacy mode and clear fdb table created flag.
So that fdb table will not be cleared again.

Fixes: f019679e

 ("net/mlx5: E-switch, Remove dependency between sriov and eswitch mode")
Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>