CLEANUP: stream_interface: stop exporting socket layer functions

Similarly to the previous patch, we don't need the socket-layer functions
outside of stream_interface. They could even move to a file dedicated to
applets, though that does not seem particularly useful at the moment.
diff --git a/src/peers.c b/src/peers.c
index 016a05f..5456410 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1177,13 +1177,12 @@
 	s->si[1].release = NULL;
 	s->si[1].send_proxy_ofs = 0;
 	set_target_proxy(&s->si[1].target, s->be);
+	stream_interface_prepare(&s->si[1], &sock_raw);
 	s->si[1].exp = TICK_ETERNITY;
 	s->si[1].flags = SI_FL_NONE;
 	if (s->be->options2 & PR_O2_INDEPSTR)
 		s->si[1].flags |= SI_FL_INDEP_STR;
 
-	stream_interface_prepare(&s->si[1], &sock_raw);
-
 	session_init_srv_conn(s);
 	set_target_proxy(&s->target, s->be);
 	s->pend_pos = NULL;