devlink: region: snapshot IDs: consolidate error values

Consolidate error codes for too big message size.

Current code is written to return -EINVAL when tailroom in the skb msg
would be exhausted precisely when it's time to nest, and return -EMSGSIZE
in all other "not enough space" conditions.

Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://patch.msgid.link/20241023131248.27192-5-przemyslaw.kitszel@intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>