Move applyUnderlyingCapabilities to ConnectivityService.

This is essentially a straighforward move of code from Vpn to
ConnectivityService, and from VpnTest to ConnectivityServiceTest.

Bug: 173331190
Test: passes existing tests, moved tests pass
Change-Id: I76daa3abcc777e9c3ba57efb750de0e2e2f3bb74
4 files changed