The file EF.AD contains the length of the MNC, this allows to phone to
distinguish where MCC/MNC end and where the MSIN number of the IMSI
begins. All cards are shipped with an MNC length of 2, which is fine for
the most situations, but when a MNC with 3 digits is needed the MNC
length value has to be updated. Otherwise the phone will recognize the
third digit of the MNC as part of the MSIN.
Related: OS#3850
