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/.gitignore b/openbsc/.gitignore
index 21b66a1..c08495f 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -69,6 +69,7 @@
 tests/trau/trau_test
 tests/mgcp/mgcp_transcoding_test
 tests/sgsn/sgsn_test
+tests/subscr/subscr_test
 
 tests/atconfig
 tests/atlocal