gsm0808: Add utils for Cell Identifier List

The planned support for true A over IP requires the encoding of
the a Cell Identifier List element (see also BSS_MAP_MSG_PAGING).

This commt adds encoding/decoding functionality and tests for
the element mentioned above, however, it is not yet actively used.

Change-Id: I625245dd1dd396fc2bc189e8cd2c444a33042528
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 323ad5a..cf0a7fe 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -150,6 +150,8 @@
 gsm0808_dec_channel_type;
 gsm0808_enc_encrypt_info;
 gsm0808_dec_encrypt_info;
+gsm0808_enc_cell_id_list;
+gsm0808_dec_cell_id_list;
 
 gsm0858_rsl_ul_meas_enc;