MINOR: connection: add names for transport and data layers

This makes debugging easier and avoids having to put ugly checks
against certain well-known internal struct pointers.
diff --git a/src/stream_interface.c b/src/stream_interface.c
index d39d764..4f93a2e 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -86,12 +86,14 @@
 	.recv    = si_conn_recv_cb,
 	.send    = si_conn_send_cb,
 	.wake    = si_conn_wake_cb,
+	.name    = "STRM",
 };
 
 struct data_cb si_idle_conn_cb = {
 	.recv    = si_idle_conn_null_cb,
 	.send    = si_idle_conn_null_cb,
 	.wake    = si_idle_conn_wake_cb,
+	.name    = "IDLE",
 };
 
 /*