WifiNetworkSelector: Minor cleanups

Changes:
a) Add an explicit type to differentiate the different evaluators rather
than implicitly relying on the order of registration.
b) Move the registration of the evaluators to WifiInjector.

Bug: 125781843
Test: ./frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Test: Will send for regression tests.
Change-Id: Icadb298ddd39aaa03412707acfb007ce23d27692
13 files changed