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/cache.c b/src/cache.c
index 0322552..020650a 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -1384,7 +1384,7 @@
 		shctx_row_inc_hot(shctx_ptr(cache), block_ptr(res));
 		shctx_unlock(shctx_ptr(cache));
 		s->target = &http_cache_applet.obj_type;
-		if ((appctx = stream_int_register_handler(&s->si[1], objt_applet(s->target)))) {
+		if ((appctx = si_register_handler(&s->si[1], objt_applet(s->target)))) {
 			appctx->st0 = HTTP_CACHE_INIT;
 			appctx->rule = rule;
 			appctx->ctx.cache.entry = res;