tcp: build tcp_sack.c and tcp_reass.c under bounds-safety

[abhijeetsharma2002_gmail.com]

Summary

Forge VNET variable pointers as single objects, bound to_sacks in
struct tcpopt by its length, and declare two tcp_reass() locals
__single. No change without the flag.

Sponsored by: The FreeBSD Foundation

[glebius]

Is the VNET change related to the TCP changes? Are TCP changes related at all?

[abhijeetsharma2002_gmail.com]

In D60830#1395907, @glebius wrote:

Is the VNET change related to the TCP changes? Are TCP changes related at all?

Yes, they're all needed for tcp_sack.c and tcp_reass.c to build with -fbounds-safety, and dropping any one of them breaks it. The vnet.h change is for the atomic ops on V_tcp_sack_globalholes in tcp_sack.c, and tcp_var.h bounds to_sacks for the SACK loop.

[rpaulo]

sys/net/vnet.h

293

This may be tricky because they may not be single…