ethernet: further cleanup updateConfiguration tests

Moving NetworkCapabilities to a global removes a bunch of boilerplate
code. In addition, eventuallyExpectCapabilities() now checks for the
(non-exlusive) presence of all specified capabilities.

Test: atest EthernetManagerTest --iterations 10
Change-Id: Ic3d0a22ec45c8be8d9a719c4d9f2291e63437578