ethernet: clean up test interface tracking

This change adds a isValidEthernetInterface() similar to
isValidTestInterface() in place of updating the interface matching
regex. This makes the code more readable.

It's unfortunate that getInterfaceList() was added as a synchronous API
making its behavior race-y around setting setIncludeTestInterfaces().

Test: atest EthernetManagerTest
Change-Id: Ib0652654020fc3f6e965de9091c5bc960d1d4cdf
1 file changed