add gsup_test to catch OS#3231

Encode an Insert Subscr Data with is_ps == true to trigger the encoding bug
described in OS#3231, i.e. show that it is fixed.

Move osmo_gsup_addr_send() to a separate .c file, so that it can be overridden
in the regression test to just dump the msgb instead.

I used this test to reproduce issue OS#3231, and now that it's here we might as
well keep it, and possibly expand on it in the future.

Related: OS#3231
Change-Id: Id1453351758f3e1a9ff03bd99fefaf51886e77da
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 74179e7..70ae7ae 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -15,6 +15,13 @@
 AT_CHECK([$abs_top_builddir/tests/auc/auc_ts_55_205_test_sets], [], [expout], [experr])
 AT_CLEANUP
 
+AT_SETUP([gsup])
+AT_KEYWORDS([gsup])
+cat $abs_srcdir/gsup/gsup_test.ok > expout
+cat $abs_srcdir/gsup/gsup_test.err > experr
+AT_CHECK([$abs_top_builddir/tests/gsup/gsup_test], [], [expout], [experr])
+AT_CLEANUP
+
 AT_SETUP([gsup_server])
 AT_KEYWORDS([gsup_server])
 cat $abs_srcdir/gsup_server/gsup_server_test.ok > expout