Update to positive logic to better match the method naming

The method checkInterfacePresent seems that should return if the
interface is present or not, but it actually return an opposite
result. It may confuse the caller. E.g. The override method in
VpnTest assume it always returns true in the test. It will fail
the vpn start flow due to interface gone.

Bug: 169215213
Test: atest FrameworksNetTess
Change-Id: I3e9a64f0900336b8205674b94db68f090b4e9ff9