tcp: fix the tcp unittest to work

Type: fix

Signed-off-by: Ryujiro Shibuya <ryujiro.shibuya@owmobility.com>
Change-Id: If5a8313262da828616db8b1d9ef831d42b11d952
diff --git a/src/plugins/unittest/tcp_test.c b/src/plugins/unittest/tcp_test.c
index 3db0405..3e5ba9c 100644
--- a/src/plugins/unittest/tcp_test.c
+++ b/src/plugins/unittest/tcp_test.c
@@ -1341,6 +1341,8 @@
 {
   int res = 0;
 
+  vnet_session_enable_disable (vm, 1);
+
   while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
     {
       if (unformat (input, "sack"))