GSM 04.08: Add support for parsing CSD related bearer capabilities

Also adds a test case for both encoder and decoder of this IE
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 69624c1..2154269 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -71,3 +71,9 @@
 cat $abs_srcdir/gsm0808/gsm0808_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/gsm0808/gsm0808_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([gsm0408])
+AT_KEYWORDS([gsm0408])
+cat $abs_srcdir/gsm0408/gsm0408_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/gsm0408/gsm0408_test], [], [expout], [ignore])
+AT_CLEANUP