net/mlx5: ft: Check prio and chain sanity for ft offload

Before changing the chain from original chain to ft offload chain,
make sure user doesn't actually use chains.

While here, normalize the prio range to that which we support.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>