[MEDIUM] use buffer_check_timeouts instead of stream_sock_check_timeouts()

It's more appropriate to use buffer_check_timeouts() to check for buffer
timeouts and si->shutw/shutr to shutdown the stream interfaces.
diff --git a/src/client.c b/src/client.c
index 32e90ba..547e215 100644
--- a/src/client.c
+++ b/src/client.c
@@ -174,6 +174,7 @@
 		s->si[0].err_type = SI_ET_NONE;
 		s->si[0].err_loc = NULL;
 		s->si[0].owner = t;
+		s->si[0].shutr = stream_sock_shutr;
 		s->si[0].shutw = stream_sock_shutw;
 		s->si[0].fd = cfd;
 		s->si[0].exp = TICK_ETERNITY;
@@ -183,6 +184,7 @@
 		s->si[1].err_type = SI_ET_NONE;
 		s->si[1].err_loc = NULL;
 		s->si[1].owner = t;
+		s->si[1].shutr = stream_sock_shutr;
 		s->si[1].shutw = stream_sock_shutw;
 		s->si[1].exp = TICK_ETERNITY;
 		s->si[1].fd = -1; /* just to help with debugging */