Fix ethernet enable / disable API

The ethernet APIs connectNetwork() / disconnectNetwork() are
inaccurately named. Physical link state cannot be changed by calling an
API. This change renames these functions to enableInterface and
disableInterface, respectively, to better reflect their intention and
behavior.

Test: atest EthernetManagerPermissionTest
Merged-In: I3361ad0e01e761ffd77faf6c55924fa4612ede90
Change-Id: I3361ad0e01e761ffd77faf6c55924fa4612ede90