tls: move test certificates to separate header file

Change-Id: I543cb78e268d7a4a7fba590d305351ec79f4e4da
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vnet/session-apps/echo_server.c b/src/vnet/session-apps/echo_server.c
index c59a233..f9d3d93 100644
--- a/src/vnet/session-apps/echo_server.c
+++ b/src/vnet/session-apps/echo_server.c
@@ -17,6 +17,7 @@
 #include <vlibmemory/api.h>
 #include <vnet/session/application.h>
 #include <vnet/session/application_interface.h>
+#include <vnet/session/session.h>
 
 typedef struct
 {