net/mlx5: LAG, generalize handling of shared FDB

Shared FDB handling is using the assumption that shared FDB can only
be created from two devices.
In order to support shared FDB of more than two devices, iterate over
all LAG ports instead of hard coding only the first two LAG ports
whenever handling shared FDB.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>