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
Merged-in: I38afd17475bbdb1dff80fbd82e70cf468dece652
Change-Id: I38afd17475bbdb1dff80fbd82e70cf468dece652
(cherry picked from commit a28bf2a4)