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