net/mlx5: Set term table as an unmanaged flow table

Termination tables are restricted to have the default miss action and
cannot be set to forward to another table in case of a miss.
If the fs prio of the termination table is not the last one in the
list, fs_core will attempt to attach it to another table.

Set the unmanaged ft flag when creating the termination table ft
and select the tc offload prio for it to prevent fs_core from selecting
the forwarding to next ft miss action and use the default one.

In addition, set the flow that forwards to the termination table to
ignore ft level restrictions since the ft level is not set by fs_core
for unamanged fts.

Fixes: 249ccc3c

 ("net/mlx5e: Add support for offloading traffic from uplink to uplink")
Signed-off-by: Ariel Levkovich <lariel@nvidia.com>