Revert the partial MFC of r313045 which broke dtrace

This removes the mbuf to ipinfo_t translator and switches tcp_autorcvbuf to
use the older mtod macro.

This was originally merged to stable/10 as part of r317375.

Reported by: markj
Reviewed by: markj, hiren
Sponsored by: Multiplay
Differential Revision: https://reviews.freebsd.org/D10769

Partial MFC r316676 and the required r313045

MFC r316676:

Use estimated RTT for receive buffer auto resizing instead of timestamps.
This is a partial MFC as stable/10 doesn't include the TCP stack
modularisation.

MFC r313045:

Add an mbuf to ipinfo_t translator to finish cleanup of mbuf passing to TCP
probes. This is a partial MFC (missing debug__output & debug__drop changes)
due to the massive amount of additional dtrace changes that would be
required for a full MFC.

Relnotes: Yes
Sponsored by: Multiplay

MFC r287807:
Remove an unneeded typedef of ip6_t from the DTrace ip provider library.

PR: 203092

MFC r287807:
Remove an unneeded typedef of ip6_t from the DTrace ip provider library.

PR: 203092