net/mlx5: Separate FDB namespace

This patch doesn't add an additional namespaces, but just separates the
naming to be used by each FDB user, bypass and kernel.
Downstream patches will actually split this up and allow to have more
than single priority for the bypass users.

Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Acked-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>