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 debugoutput & debugdrop changes)
due to the massive amount of additional dtrace changes that would be
required for a full MFC.

Relnotes: Yes
Sponsored by: Multiplay