input: ipaccess: stricter string handling in ipa_bts_id_resp
input: ipaccess: stricter string handling in ipa_bts_id_resp

These strings are locally set via the BTS configuration, not the
network, but make sure we don't overrun the buffer.

Reference: CID 1040690

osmocom/libosmo-abis,osmocom/libosmo-abis,telenoobie/libosmo-abis,osmocom/libosmo-abis,telenoobie/libosmo-abis