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: I2e633fd764f86b196a6ee0c29af2b97733e82c66
Change-Id: I2e633fd764f86b196a6ee0c29af2b97733e82c66
(cherry picked from commit db897af7)