In libosmocore Change-ID I1834d90fbcdbfcb05f5b8cfe39bfe9543737ef8f
we have introduced ipa_ccm_id_resp_parse() as a bugfixed replacement
of ipa_ccm_idtag_parse().
The main difference is that the returned "value" parts now have
a correct reported "length", whereas before this commit they all
reported a one-byte too-long "length" for each IE.
Let's use this opportunity to remove the copy+pasted
osmo_ipa_idtag_parse() function from the libosmo-netif codebase.
Change-Id: I4626d247626543e032593bf226b6c233f6678562