gsm0808: Add utils for Encryption Information

The planned support for true A over IP requires the encoding of
the an Encryption Information element (see also BSS_MAP_MSG_CIPHER_MODE_CMD).

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

Change-Id: I8262050a9d9fd3f17462cfbb046c6e034dccc6fb
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 2ba0c42..323ad5a 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -148,6 +148,8 @@
 gsm0808_dec_speech_codec_list;
 gsm0808_enc_channel_type;
 gsm0808_dec_channel_type;
+gsm0808_enc_encrypt_info;
+gsm0808_dec_encrypt_info;
 
 gsm0858_rsl_ul_meas_enc;