gsm0408_test: add a testcase for gsm48_decode_bearer_cap()

The new testcase contains a Bearer capability IE from Siemens S11E,
which does not use octet 3a (no extension bit set in octet 3).
gsm48_decode_bearer_cap() currently fails to parse it.

Change-Id: Ia19f3f6d80bc09ca3f8d39d35b148a0c0245141f
diff --git a/tests/testsuite.at b/tests/testsuite.at
index ca133bb..44ae539 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -153,7 +153,8 @@
 AT_SETUP([gsm0408])
 AT_KEYWORDS([gsm0408])
 cat $abs_srcdir/gsm0408/gsm0408_test.ok > expout
-AT_CHECK([$abs_top_builddir/tests/gsm0408/gsm0408_test], [0], [expout], [ignore])
+cat $abs_srcdir/gsm0408/gsm0408_test.err > experr
+AT_CHECK([$abs_top_builddir/tests/gsm0408/gsm0408_test], [0], [expout], [experr])
 AT_CLEANUP
 
 AT_SETUP([gsm48_rest_octets])