Fix the Preconditions dependency in EthernetNetworkSpecifier.

Ethernet service related files are going to be moved into Connectivity
module. Replace the Preconditions class in the EthernetNetworkSpecifier,
either add modules-utils-preconditions static lib dependency to fix it,
however, notice that will result in the duplicate class import when
moving ethernet stuff to p/m/Connectivity.

Bug: 210586283
Test: atest FrameworksNetTests EthernetServiceTests
Change-Id: I6163699be4126ef1b95dfb87ec9a6aba2c01195a