net/mlx5e: Lag, Only handle events from highest priority multipath entry

There could be multiple multipath entries but changing the port affinity
for each one doesn't make much sense and there should be a default one.
So only track the entry with lowest priority value.
The commit doesn't affect existing users with a single entry.

Fixes: 544fe7c2

 ("net/mlx5e: Activate HW multipath and handle port affinity based on FIB events")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>