bonding: support aggregator selection based on port priority

bonding: support aggregator selection based on port priority

Add a new ad_select policy 'port_priority' that uses the per-port
actor priority values (set via ad_actor_port_prio) to determine
aggregator selection.

This allows administrators to influence which ports are preferred
for aggregation by assigning different priority values, providing
more flexible load balancing control in LACP configurations.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20250902064501.360822-3-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>