Rename rfc6675_pipe to sack.revised, and enable by default

[rscheff]

Summary

All missing pieces to claim full RFC6675 support are in place,
but disabled by default. These algorithms are all fenced
behind the preexisting sysctl "rfc6675_pipe" (disabled by default).

It was noted earlier, that referencing RFCs directly in sysctls is
not the optimal choice.

To better reflect these mechanisms belonging with SACK loss
recovery, shuffling the sysctl into the net.inet.tcp.sack branch,
and rename it to "revised".

Further, to get some additional testing coverage, enabling by default
in HEAD, by mid-march.

Unless this change (or the change of defaults) has to be backed out,
planning for an MFC to stable/13 mid-april.

[tuexen]

Any chance to have a more specific name than newsack?

[rscheff]

Certainly, I'm definitely open to suggestions. functional descriptions would be a mouthful, as 6675 has pipe, faster_lossrecovery, and rescue_rexmit.

rfc6675 was adopted in 2012... "sack2012"? Only "improved"? retain "rfc6675"? "lessrto"?

[rscheff]

• change pretty name of sysctl to 'revised'
• rebase to include PRR pipe calculation

[kbowling]

Thanks for doing this!

[kbowling]

sys/netinet/tcp_input.c

2640

This hunk fails too

sys/netinet/tcp_sack.c

835

This hunk rejected by patch, tcp_sack_partialack doesn't look like this in head

[rscheff]

• changing vnet 6675_pipe to newsack
• rename and shuffle rfc6675_pipe to sack.newsack
• onboard the cc modules to the change
• rebase to HEAD

[rscheff]

• rebase to HEAD
• make old OID read-only with a warning message

[rscheff]

transport call: Just remove old sysctl, add pointer in man page

[rscheff]

• remove sysctlproc with hint, only mention change in man page