tls: fix multi threaded medium scale test (VPP-1457)

- ensure session enqueue epoch does not wrap between two enqueues
- use 3 states for echo clients app, to distinguish between starting and
closing phases
- force tcp fin retransmit if out of buffers while sending a fin

Change-Id: I6f2cab46affd1148aba2a33fb6d58bcc54f32805
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/tls/tls.c b/src/vnet/tls/tls.c
index aba7919..9a82360 100644
--- a/src/vnet/tls/tls.c
+++ b/src/vnet/tls/tls.c
@@ -119,6 +119,7 @@
     {
       clib_rwlock_writer_lock (&tm->half_open_rwlock);
       pool_get (tm->half_open_ctx_pool, ctx);
+      ctx_index = ctx - tm->half_open_ctx_pool;
       clib_rwlock_writer_unlock (&tm->half_open_rwlock);
     }
   else
@@ -126,10 +127,10 @@
       /* reader lock assumption: only main thread will call pool_get */
       clib_rwlock_reader_lock (&tm->half_open_rwlock);
       pool_get (tm->half_open_ctx_pool, ctx);
+      ctx_index = ctx - tm->half_open_ctx_pool;
       clib_rwlock_reader_unlock (&tm->half_open_rwlock);
     }
   memset (ctx, 0, sizeof (*ctx));
-  ctx_index = ctx - tm->half_open_ctx_pool;
   return ctx_index;
 }
 
@@ -254,6 +255,8 @@
     {
       TLS_DBG (1, "failed to notify app");
       tls_disconnect (ctx->tls_ctx_handle, vlib_get_thread_index ());
+      session_free_w_fifos (app_session);
+      return -1;
     }
 
   session_lookup_add_connection (&ctx->connection,