tcp builtin_client: bug correction and short_help

The missing call to `vnet_session_enable_disable' would cause segfaults
because of an uninitialized session pointer. Just as in the builtin
server the session needs to be enabled for the client.

The `short_help' of the CLI command was also populated with the
arguments that are accepted in the parsing function
`test_tcp_clients_command_fn'.

Change-Id: I88c16efa80597dd19b406e8cf1c87aec1ec73573
Signed-off-by: Clement Durand <clement.durand@polytechnique.edu>
Signed-off-by: Pierre Pfister <ppfister@cisco.com>
diff --git a/src/vnet/tcp/builtin_client.c b/src/vnet/tcp/builtin_client.c
index c1567aa..9e8e156 100644
--- a/src/vnet/tcp/builtin_client.c
+++ b/src/vnet/tcp/builtin_client.c
@@ -419,6 +419,7 @@
 	}
     }
 #endif
+  vnet_session_enable_disable (vm, 1 /* turn on TCP, etc. */ );
 
   /* Fire off connect requests, in something approaching a normal manner */
   for (i = 0; i < n_clients; i++)
@@ -455,7 +456,7 @@
 VLIB_CLI_COMMAND (test_clients_command, static) =
 {
   .path = "test tcp clients",
-  .short_help = "test tcp clients",
+  .short_help = "test tcp clients [nclients %d] [iterations %d] [bytes %d] [uri tcp://1.2.3.4/1234]",
   .function = test_tcp_clients_command_fn,
 };
 /* *INDENT-ON* */