net/mlx5: E-switch, Destroy legacy fdb table when needed

The cited commit removes eswitch mode none. But when disabling
sriov in legacy mode or changing from switchdev to legacy mode
without sriov enabled, the legacy fdb table is not destroyed.

It is not the right behavior. Destroy legacy fdb table in above
two caes.

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>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>