The soisconnected() call removed from syncache_socket() in r307966 was

not extraneous in the TCP Fast Open (TFO) passive-open case.  In the
TFO passive-open case, syncache_socket() is being called during
processing of a TFO SYN bearing a valid cookie, and a call to
soisconnected() is required in order to allow the application to
immediately consume any data delivered in the SYN and to have a chance
to generate response data to accompany the SYN-ACK.  The removal of
this call to soisconnected() effectively converted all TFO passive
opens to having the same RTT cost as a standard 3WHS.

This commit adds a call to soisconnected() to syncache_tfo_expand() so
that it is only in the TFO passive-open path, thereby restoring TFO
passve-open RTT performance and preserving the non-TFO connection-rate
performance gains realized by r307966.

MFC after:	1 week
Sponsored by:	Limelight Networks

sys/netinet/tcp_syncache.c

@@ -1195,6 +1195,7 @@ syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 		TCPSTAT_INC(tcps_sc_aborted);
 		atomic_subtract_int(pending_counter, 1);
 	} else {
+		soisconnected(*lsop);
 		inp = sotoinpcb(*lsop);
 		tp = intotcpcb(inp);
 		tp->t_flags |= TF_FASTOPEN;