[Bonding Draft Proposal] Add lacp_prio Support for ad_select?

[Hangbin Liu <liuhangbin@gmail.com>]

Hi Jay,

We have a customer setup involving two separate switches with identical
L2/VLAN configurations. Each switch forms an independent aggregator
(port-channel), and the end host connects to both with the same number of
links and equivalent bandwidth.

As a result, the host ends up with two aggregators under a single bond
interface. Since the user cannot arbitrarily override port count or
bandwidth, they are asking for a new mechanism, lacp_prio, to influence
aggregator selection via ad_select.

Do you think this is a reasonable addition?

If yes, what would be the best way to compare priorities?

1. Port Priority Only. Currently initialized to 0xff. We could add a parameter
   allowing users to configure it.
   a) Use the highest port priority within each aggregator for comparison
   b) Sum all port priorities in each aggregator and compare the totals

2. Full LACP Info Comparison. Compare fields such as system_priority, system,
   port_priority, port_id, etc.

At present, the libteam code has implemented an approach that selects the
aggregator based on the highest system_priority/system from both local and
partner data.[1]

Looking forward to your thoughts.

Best regards,
Hangbin

[1] https://github.com/jpirko/libteam/blob/master/teamd/teamd_runner_lacp.c#L402