Fix data call issue due to improper mnc length

When apn list is created before EF_AD sim record is read,
operator numeric value is not set due to bad mnc length.
Due to this, apn list cannot be created leading to data call failure.
As EF_AD sim record is not considered as essential sim records,
apn list creation can be triggered before EF_AD record is read

Fix is to add EF_AD sim record to essential sim records list

CRs-Fixed: 2608773

Change-Id: I24a9ace85413b120ebc174a9e66930ade46aea76