Hide APNs with type="ia" and apn=""

APNs with type="ia" and no APN address (apn="") are used to
prevent an initial attach APN from being sent to the modem. This
in turn prevents the LTE ESM information procedure from being
used during the LTE attach. These APNs are meaningless and confusing to end users - so this
change hides them from the APN list.

Bug: 19101183
Change-Id: I9aacf787f8c175a301ad546f972f8972aad2a6b3