re-introduce ipa_ccm_idtag_parse_off()

In the previous commit we deprecated ipa_ccm_idtag_parse() but
also removed ipa_ccm_idtag_parse_off(), for which I couldn't find
any users.  However, legacy openbsc.git still uses this function,
so let's re-introiduce it in its original form.

Change-Id: Ibfe53b04340eb355c8bfb8453a2af1522a4b6baf
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a1d342a..2bb9d97 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -461,6 +461,7 @@
 ipa_ccm_tlv_to_unitdata;
 ipa_ccm_idtag_name;
 ipa_ccm_idtag_parse;
+ipa_ccm_idtag_parse_off;
 ipa_ccm_id_get_parse;
 ipa_ccm_id_resp_parse;
 ipa_ccm_make_id_resp;