Same structure as used for error_reply, to contain information (like path MTU or redirect gateway) from the original error packet, so that upper layers don't have to re-parse it. Nothing uses or passes it around at present, but it will be used in the next commits. Change-Id: I38a3dec5506bdcb77a7850294082db7be74dd80f Reviewed-on: https://review.haiku-os.org/c/haiku/+/9399 Reviewed-by: waddlesplash <[email protected]> Tested-by: Commit checker robot <[email protected]> Reviewed-by: Jérôme Duval <[email protected]>