bsc/test: Add tests for gsm_subscriber base

This commit adds test for the generic part of gsm_subscriber like
reference counting and flag usage.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/subscr/subscr_test.ok b/openbsc/tests/subscr/subscr_test.ok
new file mode 100644
index 0000000..72a3769
--- /dev/null
+++ b/openbsc/tests/subscr/subscr_test.ok
@@ -0,0 +1,3 @@
+Testing subscriber core code.
+Test subscriber allocation and deletion
+Done