MINOR: session: add a streams field to the session struct

This will be used to hold the list of streams belonging to a given session.
diff --git a/include/types/session.h b/include/types/session.h
index 62c3a95..35a17e1 100644
--- a/include/types/session.h
+++ b/include/types/session.h
@@ -40,6 +40,7 @@
 struct session {
 	struct proxy *fe;               /* the proxy this session depends on for the client side */
 	struct listener *listener;      /* the listener by which the request arrived */
+	struct list streams;            /* list of streams attached to this session */
 	enum obj_type *origin;          /* the connection / applet which initiated this session */
 	struct timeval accept_date;     /* date of the session's accept() in user date */
 	struct timeval tv_accept;       /* date of the session's accept() in internal date (monotonic) */