unittest: fix coverity 274736

Free up the vapi context in case of failure.

Type: fix
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: I4f64e8718014d714f1b82877e69d2354b5fa44fb

src/plugins/unittest/api_test.c

@@ -38,6 +38,7 @@ connect_to_vpp (void)
 			     true) != VAPI_OK)
     {
       clib_warning ("vapi_connect failed");
+      vapi_ctx_free (ctx);
       return 0;
     }
   return ctx;