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/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 6ad363f..6795c57 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -791,5 +791,11 @@
 osmo_iuup_rnl_prim_alloc;
 osmo_iuup_tnl_prim_alloc;
 
+osmo_csd_12k_6k_decode_frame;
+osmo_csd_12k_6k_encode_frame;
+osmo_csd_3k6_decode_frame;
+osmo_csd_3k6_encode_frame;
+osmo_csd_ubit_dump;
+
 local: *;
 };