session: improve close procedure

Change-Id: I6201a044e70ab6a58db8212960c57edc77c41f96
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/session/stream_session.h b/src/vnet/session/stream_session.h
index b08f959..30178d7 100644
--- a/src/vnet/session/stream_session.h
+++ b/src/vnet/session/stream_session.h
@@ -31,6 +31,7 @@
   SESSION_STATE_ACCEPTING,
   SESSION_STATE_READY,
   SESSION_STATE_OPENED,
+  SESSION_STATE_TRANSPORT_CLOSING,
   SESSION_STATE_CLOSING,
   SESSION_STATE_CLOSED,
   SESSION_STATE_N_STATES,