Process all layers before SRH in packet order in endpoints

[louisroyer]

to follow RFC 8200. "a receiver must not, for example, scan through a packet looking for a particular kind of extension header and process that header prior to processing all preceding ones."

In particular before the SRH:

• if Hop by Hop option -> don't process the header ("it is now expected that nodes along a packet's delivery path only examine and process the Hop-by-Hop Options header if explicitly configured to do so.")
• if Fragments -> drop + icmp: routers must not fragment/reassemble packets
• if Destination Options -> depends on 2 first bits of each included Option Type
• if Authentication -> drop + icmp: unsupported
• if Encapsulating Security Payload -> drop + icmp: unsupported
• if unrecognized -> send an ICMP Parameter Problem message to the source of
  the packet, with an ICMP Code value of 1 ("unrecognized Next Header
  type encountered") and the ICMP Pointer field containing the offset
  of the unrecognized value within the original packet.

Layers after SRH are considered payload, independently of the Next Header, and therefore are not processed.