vcl/session: apps with process workers

Allow apps to register child processes as app workers. In particular,
on fork vcl now registers the child process with vpp as a new worker.

Change-Id: I52a65fbc3292962b1f6e1fe0f6153f739e6e0d4a
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/session/application_interface.c b/src/vnet/session/application_interface.c
index 89f7462..3cd8c2f 100644
--- a/src/vnet/session/application_interface.c
+++ b/src/vnet/session/application_interface.c
@@ -554,7 +554,7 @@
     }
 
   app_interface_check_thread_and_barrier (vnet_application_detach, a);
-  application_free (app);
+  application_detach_process (app, a->api_client_index);
   return 0;
 }