devlink: Add port-specific option to resource dump doit

devlink: Add port-specific option to resource dump doit

Allow querying devlink resources per-port via the resource-dump doit
handler. When a port-index attribute is provided, only that port's
resources are returned. When no port-index is given, only device-level
resources are returned, preserving backward compatibility.

Signed-off-by: Or Har-Toov <ohartoov@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260407194107.148063-8-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>