Sometimes getmac lists many interfaces for the same MAC address,
while Interfaces returns only single name for that address. Adjust
the test to ignore the names that are not returned by the Interfaces.

Fixes #21027

Change-Id: I08d98746a7c669f2d730dba2da36e07451a6f405
Reviewed-on: https://go-review.googlesource.com/59411Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>