gbproxy/test: Fix time calculation in test_gbproxy_tlli_expire()

A single test case still uses time() to obtain the reference time.

This commit fixes this by using the 'now' variable instead, that
contains a fixed time value and does therefore not depend on when the
test is executed.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index 6ac1ae9..df7b22e 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -3780,7 +3780,7 @@
 		register_tlli(peer, tlli2, imsi2, ARRAY_SIZE(imsi2), now);
 		OSMO_ASSERT(peer->patch_state.logical_link_count == 2);
 
-		num_removed = gbproxy_remove_stale_link_infos(peer, time(NULL) + 2);
+		num_removed = gbproxy_remove_stale_link_infos(peer, now + 2);
 		OSMO_ASSERT(num_removed == 1);
 		OSMO_ASSERT(peer->patch_state.logical_link_count == 1);