devlink: introduce a helper for netlink multicast send

Introduce a helper devlink_nl_notify_send() so each object notification
function does not have to call genlmsg_multicast_netns() with the same
arguments.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

devlink: send notifications only if there are listeners

Introduce devlink_nl_notify_need() helper and using it to check at the
beginning of notification functions to avoid overhead of composing
notification messages in case nobody listens.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

devlink: rename netlink callback to be aligned with the generated ones

All remaining doit and dumpit netlink callback functions are going to be
used by generated split ops. They expect certain name format. Rename the
callback to be aligned with generated names.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231021112711.660606-8-jiri@resnulli.us
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

devlink: push param related code into separate file

Cut out another chunk from leftover.c and put param related code
into a separate file.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20230828061657.300667-8-jiri@resnulli.us
Signed-off-by: Jakub Kicinski <kuba@kernel.org>