MINOR: connection: introduce conn_stream

This patch introduces a new struct conn_stream. It's the stream-side of
a multiplexed connection. A pool is created and destroyed on exit. For
now the conn_streams are not used at all.
diff --git a/include/types/obj_type.h b/include/types/obj_type.h
index a6310cf..e141d69 100644
--- a/include/types/obj_type.h
+++ b/include/types/obj_type.h
@@ -40,6 +40,7 @@
 	OBJ_TYPE_APPCTX,       /* object is a struct appctx */
 	OBJ_TYPE_CONN,         /* object is a struct connection */
 	OBJ_TYPE_SRVRQ,        /* object is a struct dns_srvrq */
+	OBJ_TYPE_CS,           /* object is a struct conn_stream */
 	OBJ_TYPE_ENTRIES       /* last one : number of entries */
 } __attribute__((packed)) ;