MINOR: session: store the session's accept date

Doing so ensures we don't need to use the stream anymore to prepare the
log information to report a failed handshake on an embryonic session.
Thus, prepare_mini_sess_log_prefix() now takes a session in argument.
diff --git a/include/types/session.h b/include/types/session.h
index 6f26ca9..e4e393b 100644
--- a/include/types/session.h
+++ b/include/types/session.h
@@ -39,6 +39,8 @@
 	struct proxy *fe;               /* the proxy this session depends on for the client side */
 	struct listener *listener;      /* the listener by which the request arrived */
 	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) */
 };
 
 #endif /* _TYPES_SESSION_H */