Backport the new TCP reassembly code from head to stable/11.

In particular:

• Cherry pick the changes in sys/queue.h from r334804.

• MFC r338102 with manually removing changes to file not existent in stable/11 and resolve conflicts in tcp_var.h. This change represents a substantial restructure of the way we reassembly inbound tcp segments. The old algorithm just blindly dropped in segments without coalescing. This meant that every segment could take up greater and greater room on the linked list of segments. This of course is now subject to a tighter limit (100) of segments which in a high BDP situation will cause us to be a lot more in-efficent as we drop segments beyond 100 entries that we receive. What this restructure does is cause the reassembly buffer to coalesce segments putting an emphasis on the two common cases (which avoid walking the list of segments) i.e. where we add to the back of the queue of segments and where we add to the front. We also have the reassembly buffer supporting a couple of debug options (black box logging as well as counters for code coverage). These are compiled out by default but can be added by uncommenting the defines.

• Manually fix tcp_stacks/fastopen.c, since it does not exist anymore in head.

• MFC r342280: Fix a regression in the TCP handling of received segments. When receiving TCP segments the stack protects itself by limiting the resources allocated for a TCP connections. This patch adds an exception to these limitations for the TCP segement which is the next expected in-sequence segment. Without this patch, TCP connections may stall and finally fail in some cases of packet loss.

• MFC r343439: Don't include two header files when not needed. This allows the part of the rewrite of TCP reassembly in this files to be MFCed to stable/11 with manual change.

• MFC r344428: This patch addresses an issue brought up by bz@ in D18968: When TCP_REASS_LOGGING is defined, a NULL pointer dereference would happen, if user data was received during the TCP handshake and BB logging is used. A KASSERT is also added to detect tcp_reass() calls with illegal parameter combinations.

Reviewed by: bz@, jtl, rrs@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D18960