hsl: BTS support

This patch adds the BTS support for the hsl driver.

It includes two examples under the tests/ directory.
diff --git a/src/ipa_proxy.c b/src/ipa_proxy.c
index 2ad4654..c79b544 100644
--- a/src/ipa_proxy.c
+++ b/src/ipa_proxy.c
@@ -188,6 +188,7 @@
 	conn->dst = ipa_client_link_create(NULL, NULL, NULL, 0,
 					   route->shared->dst.inst->net.addr,
 					   route->shared->dst.inst->net.port,
+					   NULL,
 					   ipa_sock_dst_cb,
 					   ipa_client_write_default_cb,
 					   conn);