net/mlx5: LAG, prepare for SD device integration

net/mlx5: LAG, prepare for SD device integration

Socket Direct (SD) secondaries devices will participate in LAG, even
though they are silent. SD secondary devices share the same physical
port as their primary but are separate PCI functions that need to be
tracked alongside regular LAG ports.

Extend lag_func with a group_id field to identify SD group membership
and introduce a unified iterator that can filter by group. Add APIs
for registering SD secondary devices in an existing LAG.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260531113954.395443-6-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>