mod_bosh: Include stream attributes in stream-features event

This matches what mod_c2s does, and fixes a traceback in mod_sasl2_fast when
used with BOSH (that module tries to use event.stream.from).

plugins/mod_bosh.lua

@@ -456,7 +456,7 @@ function stream_callbacks.streamopened(context, attr)
 
 	if session.notopen then
 		local features = st.stanza("stream:features");
-		module:context(session.host):fire_event("stream-features", { origin = session, features = features });
+		module:context(session.host):fire_event("stream-features", { origin = session, features = features, stream = attr });
 		session.send(features);
 		session.notopen = nil;
 	end