tcp: clear SACK state when scoreboard is forcefully freed

[rscheff]

Summary

When a RTO happens during an on-going SACK loss recovery
episode, the internal summary accounting is not cleared.
This may lead to subsequent errors in calculations
(e.g. IsLost()).

PR: 274406
Reported by: pho

[cc]

sys/netinet/tcp_sack.c

891

Better keep the fields in order like in the struct sackhint definition.

tp->sackhint.delivered_data = 0;
tp->sackhint.sacked_bytes = 0;
tp->sackhint.hole_bytes = 0;
tp->sackhint.lost_bytes = 0;

[pho]

This change fixes the panic I saw.

[rscheff]

sys/netinet/tcp_sack.c

891

I trust gcc to do simple reorders like this for more effective data access. Already committed to fix an ongoing panic.