MINOR: peers: use the socket layer operations from the peer instead of sock_raw

At the moment, all the peers are initialized to use sock_raw as the socket
layer, so use this info in peers_session_create() instead of the hard-coded
sock_raw.
diff --git a/src/peers.c b/src/peers.c
index 721eecb..c615b3b 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1177,7 +1177,7 @@
 	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);
+	stream_interface_prepare(&s->si[1], peer->sock);
 	s->si[1].exp = TICK_ETERNITY;
 	s->si[1].flags = SI_FL_NONE;
 	if (s->be->options2 & PR_O2_INDEPSTR)