Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r235944:

Significantly update tcp_lro for mostly two things:
1) introduce basic support for IPv6 without extension headers.
2) try hard to also get the incremental checksum updates right,
especially also in the IPv4 case for the IP and TCP header.

Move variables around for better locality, factor things out into
functions, allow checksum updates to be compiled out, ...

Leave a few comments on further things to look at in the future,
though that is not the full list.

Update drivers with appropriate #includes as needed for IPv6 data
type in LRO.

Approved by: re

MFC r235474:

Switch to a standard 2 clause BSD license (from bsd-style-copyright).

Approved by: Myricom Inc. (gallatin)
Approved by: Intel Corporation (jfv)

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Trim extra spaces before tabs.

Add generic TCP LOR into netinet