Load APN configure file from product image preferentially instead of system image

According to the current logic of loading APN configure file, loaded from system image as default,there exist problems under such circumstance:

If system image is fixed on customer version. APN configure file could not be modified for customization.

Therefore, we suggest that chagne the logic of load APN configures file to loading APN configure file from product image preferentially instead of system image.

Bug: 120805875
Test: Check the path of APN configure file in phone
Change-Id: I595b50e975613cf775b521401644ae426bcd0703
1 file changed