Fix attach issue due to wrong attach apn

If there are no apns defined for operator, emergency apn read from
apn database during powerup will be used for set initial attach request.
Network may reject attach request if attach apn is improper.
Fix is to send empty apn whenever there is only emergency apn of other
mcc-mnc available for set initial attach apn request

Change-Id: I087c75b59952ec00661d3f492639043282cd779f
CRs-Fixed: 2324090