CLEANUP: stream-int: consistently call the si/stream_int functions

As long-time changes have accumulated over time, the exported functions
of the stream-interface were almost all prefixed "si_<something>" while
most private ones (mostly callbacks) were called "stream_int_<something>".
There were still a few confusing exceptions, which were addressed to
follow this shcme :
  - stream_sock_read0(), only used internally, was renamed stream_int_read0()
    and made static
  - stream_int_notify() is only private and was made static
  - stream_int_{check_timeouts,report_error,retnclose,register_handler,update}
    were renamed si_<something>.

Now it is clearer when checking one of these if it risks to be used outside
or not.
diff --git a/src/proto_http.c b/src/proto_http.c
index 100a7ba..71609f2 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -140,7 +140,7 @@
 
 	s->txn->flags &= ~TX_WAIT_NEXT_RQ;
 	FLT_STRM_CB(s, flt_http_reply(s, status, msg));
-	stream_int_retnclose(&s->si[0], msg);
+	si_retnclose(&s->si[0], msg);
 }
 
 /* Parse the URI from the given transaction (which is assumed to be in request
@@ -2577,7 +2577,7 @@
 	 */
 	if (stats_check_uri(&s->si[1], txn, px)) {
 		s->target = &http_stats_applet.obj_type;
-		if (unlikely(!stream_int_register_handler(&s->si[1], objt_applet(s->target)))) {
+		if (unlikely(!si_register_handler(&s->si[1], objt_applet(s->target)))) {
 			txn->status = 500;
 			s->logs.tv_request = now;
 			http_reply_and_close(s, txn->status, http_error_message(s));