Use BpfDump#fromBase64EncodedString

aosp/2179274 adds fromBase64EncodedString to BpfDump.
This CL updates EthernetTetheringTest to use this function instead of
parseMapKeyValue in EthernetTetheringTest.

Bug: 217624062
Test: atest EthernetTetheringTest
Change-Id: I56b3cd875e16bee6174f0aacd468562ae482cef9
1 file changed