[SP18.1] add dependency object to OffloadController

In order to mock constant in unit test, a dependency object is
introduced with minimum code change to achieve this.

Test: atest TetheringTests
Bug: 149467454
Change-Id: I38628daddcb7be7c74846e78d36dc88f065b97d9
Merged-In: I38628daddcb7be7c74846e78d36dc88f065b97d9
(cherry picked from commit 7eff4acc9e051e5360526cbc4d80964198b6d73e)
3 files changed