conv: add convolutional coder for AMR SID UPDATE frames

AMR SID update frames are protected using an 1/4 convolutional coder,
wich is similar to the one used with 6,7 kbit voice frames. Except that
there is no puncturing and the length is different.

Change-Id: Ia35ed4178a7f0d816052b7e5d6478b93a1d9744f
Related: OS#2978
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index efca0a5..a518b28 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -135,6 +135,7 @@
 gsm0503_tch_ahs_5_9;
 gsm0503_tch_ahs_5_15;
 gsm0503_tch_ahs_4_75;
+gsm0503_tch_axs_sid_update;
 gsm0503_mcs1_dl_hdr;
 gsm0503_mcs1_ul_hdr;
 gsm0503_mcs1;