gbproxy: Parse Attach Reject messages

That message is currently ignored but should invalidate the TLLI and
de-register the logical link instead.

This patch extends the parser to recognize such messages and to set
the invalidate_tlli flag.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index 9b2218c..a128b39 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -3418,6 +3418,8 @@
 
 	dump_peers(stdout, 0, 0, &gbcfg);
 
+	OSMO_ASSERT(!gbproxy_link_info_by_tlli(peer, foreign_tlli));
+
 	/* Attach (incomplete) and Detach (MO) */
 
 	gbproxy_delete_link_infos(peer);
diff --git a/openbsc/tests/gbproxy/gbproxy_test.ok b/openbsc/tests/gbproxy/gbproxy_test.ok
index f37443b..16e9d48 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.ok
+++ b/openbsc/tests/gbproxy/gbproxy_test.ok
@@ -5487,7 +5487,7 @@
     Attach Reject count             : 1
     TLLI cache size                 : 1
     TLLI-Cache: 1
-      TLLI afe2b700 -> afe2b700, IMSI 12131415161718, AGE 0
+      TLLI 00000000, IMSI 12131415161718, AGE 0, DE-REGISTERED
 PROCESSING ATTACH REQUEST from 0x01020304:1111
 00 00 10 02 01 af e2 b7 00 00 00 04 08 88 11 22 33 40 50 60 12 34 00 80 0e 00 34 01 c0 51 08 01 02 f5 e0 21 08 02 05 f4 fb c5 46 79 11 22 33 40 50 60 19 18 b3 43 2b 25 96 62 00 60 80 9a c2 c6 62 00 60 80 ba c8 c6 62 00 60 80 00 a0 bd 72