gsm: TS 44.021 modified V.110 frame encoding/decoding support

3GPP TS 44.021 specifies the format for modified V.110 frames as used
on the GSM air (radio) interface.  Implement encoders and decoders for
this modified V.110 format.

Related: OS#1572
Change-Id: I60a2f2690459359437df20cf4da9043fa7c3ad11
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 39cf54a..60aa74d 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -502,3 +502,9 @@
 cat $abs_srcdir/v110/test_ra1.ok > expout
 AT_CHECK([$abs_top_builddir/tests/v110/test_ra1], [], [expout],[])
 AT_CLEANUP
+
+AT_SETUP([gsm44021_test_frame_csd])
+AT_KEYWORDS([gsm44021_test_frame_csd])
+cat $abs_srcdir/gsm44021/test_frame_csd.ok > expout
+AT_CHECK([$abs_top_builddir/tests/gsm44021/test_frame_csd], [], [expout],[])
+AT_CLEANUP