Module Name:	src
Committed By:	thorpej
Date:		Wed Sep  9 01:32:28 UTC 1998

Modified Files:
	src/sys/netinet: tcp_input.c tcp_var.h
Log Message:
Use an algorithm similar to that in tcp_notify() to determine if
syn_cache_unreach() should remove the entry, or just continue on.

Algorithm is to only remove the entry if we've had more than one unreach
error and have retransmitted 3 or more times.  This prevents the following
scenario, as noted in PR #5909 (PR from Ty Sarna, scenario from
Charles Hannum):

* Host A sends a SYN.
* Host A retransmits the SYN.
* Host B gets the first SYN and sends a SYN-ACK.
* Host B gets the second SYN and sends a SYN-ACK.
* One of the SYN-ACK bounces with an
ICMP unreachable, causing the `SYN cache' entry to be
removed with no notification.
* Host A receives the other SYN-ACK, sends an ACK, and goes to
ESTABLISHED state.

Should fix PR #5909.