Don't drop options from the third retransmitted SYN by default.  If the SYNs (or SYN/ACK replies) are dropped due to network congestion, then the remote end of the connection may act as if options such as window scaling are enabled but the local end will think they are not.  This can result in very slow data transfers in the case of window scaling disagreements.
Don't drop options from the third retransmitted SYN by default.  If the
SYNs (or SYN/ACK replies) are dropped due to network congestion, then the
remote end of the connection may act as if options such as window scaling
are enabled but the local end will think they are not.  This can result in
very slow data transfers in the case of window scaling disagreements.

The old behavior can be obtained by setting the
net.inet.tcp.rexmit_drop_options sysctl to a non-zero value.

Reviewed by:	net@
MFC after:	2 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase