Don't run EthernetTetheringTest if Ethernet is not supported

Bug: 288844185
Test: atest CtsTetheringTest
(cherry picked from https://android-review.googlesource.com/q/commit:dc581e6c8ff1a5b956ba41b2eb1fcdc7a11e1e65)
Merged-In: Ie918a0657ab17900437918f7ae99f7aa2539052c
Change-Id: Ie918a0657ab17900437918f7ae99f7aa2539052c
1 file changed