session: free session after transport and app confirm

In addition to that, a bit of refactoring.

Change-Id: Iea1eabc2167bcdef185ec53bc09bae087c5398e6
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/udp/udp.c b/src/vnet/udp/udp.c
index 8c2daaf..7674ef2 100644
--- a/src/vnet/udp/udp.c
+++ b/src/vnet/udp/udp.c
@@ -168,7 +168,7 @@
     {
       udp_unregister_dst_port (vm, clib_net_to_host_u16 (uc->c_lcl_port),
 			       uc->c_is_ip4);
-      stream_session_delete_notify (&uc->connection);
+      session_transport_delete_notify (&uc->connection);
       udp_connection_free (uc);
     }
 }