Disable DUN APN while roaming for certain carriers

Some carriers would like to use default APN for
tethering while the device is roaming. Added a new
carrier config to disable DUN APN while the device
is roaming.

Fix: 158546796
Test: DcTrackerTest
Change-Id: I2c05398db8ecd1f85e82aed39a8964d2679765ca