sysctl.7: add various networking-related nodes
There are probably more to add (certainly across all the top-level node
categories), but these cover (or are related to) a few that frequently
get mentioned in performance tuning blog posts and emails.
(Confusingly, some lists are alphabetical and others aren't. I added the
TCP autosizing entries where they seemed to logically go.)
tcp_usrreq.c: minor sysctl description updates
TCP buffer autosizing can't really be deemed "experimental" since it was
enabled by default in early 2010.
virtio(4): improve text and remove technical details not relevant to users.
Do not mention virtio_mmio directly.
Simplify wording were possible.
pv(4) usage examples and author credits should likely be added in the future.
Changes discussed with uwe@
No full concensus, but better than previous version.
Make sure the stack is aligned when delivering signals.
Fixes the t_signal_and_sp:misaligned_sp_and_signal and
t_signal_and_sp:signalsp_sigaltstack test cases on m68k.