session: add support for memfd segments

- update segment manager and session api to work with both flavors of
  ssvm segments
- added generic ssvm slave/master init and del functions
- cleanup/refactor tcp_echo
- fixed uses of svm fifo pool as vector

Change-Id: Ieee8b163faa407da6e77e657a2322de213a9d2a0
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/session/application_interface.h b/src/vnet/session/application_interface.h
index 68973a9..8db318f 100644
--- a/src/vnet/session/application_interface.h
+++ b/src/vnet/session/application_interface.h
@@ -39,9 +39,7 @@
   /*
    * Results
    */
-  u8 *segment_name;
-  u32 segment_name_length;
-  u32 segment_size;
+  ssvm_private_t *segment;
   u64 app_event_queue_address;
   u32 app_index;
 } vnet_app_attach_args_t;