vcl: add support for app socket api

To enable add "app-socket-api /path/to/socket" to vcl.conf. On vpp side, add
use-app-socket-api to session stanza in startup.conf

VPP allocates a socket per application namespace which it places in the
app_ns_sockets subfolder of the run folder (default /var/run/vpp). The
socket used implicitly selects the app namespace for the vcl app.

Type: feature

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: Ifc14b93dcbf6ef9bed1852d46cd069f4855b92ef
diff --git a/src/vcl/CMakeLists.txt b/src/vcl/CMakeLists.txt
index ab0a6ad..e6d8f98 100644
--- a/src/vcl/CMakeLists.txt
+++ b/src/vcl/CMakeLists.txt
@@ -21,6 +21,7 @@
   vcl_cfg.c
   vcl_private.c
   vcl_locked.c
+  vcl_sapi.c
 
   LINK_LIBRARIES
   vppinfra svm vlibmemoryclient rt pthread