MINOR: listener: prefer to retrieve the socket's settings via the receiver

Some socket settings used to be retrieved via the listener and the
bind_conf. Now instead we use the receiver and its settings whenever
appropriate. This will simplify the removal of the dependency on the
listener.
diff --git a/src/session.c b/src/session.c
index 58eacd4..c5af3c4 100644
--- a/src/session.c
+++ b/src/session.c
@@ -153,7 +153,7 @@
 	cli_conn->handle.fd = cfd;
 	*cli_conn->src = *addr;
 	cli_conn->flags |= CO_FL_ADDR_FROM_SET;
-	cli_conn->proxy_netns = l->bind_conf->settings.netns;
+	cli_conn->proxy_netns = l->rx.settings->netns;
 
 	conn_prepare(cli_conn, l->rx.proto, l->bind_conf->xprt);
 	conn_ctrl_init(cli_conn);