Translation in the v6->v4 direction does not need L4 info, get rid of it.
Factor out the fill-in of a new IPv4 header from IPv6 header
Remove extraneous whitespace
Make the update of ICMPv6 type/code checksum-updating too
fix the typo in the icmph->icmp6h while doing the previous change
Add debugging of checksum update and the update itself.
remove L4 IDs on the v6->v4 translation path
Add a temporary band-aid to set the transport header.
Move to using incremental checksum adjustment in the v6->v4 direction.
V4 packets end up being 14 bytes less since the device does not need the ethernet header.
Get rid of reassembly - we can now translate incrementally, so no need to keep the full packet.