Add TetheredClient tests

Test APIs below:
getAddresses()
getMacAddress()
getTetheringType()
AddressInfo.getAddress()
AddressInfo.getHostname()
AddressInfo.writeToParcel(android.os.Parcel, int)

Bug: 153614365
Bug: 153613717
Test: atest TetheringTests
Change-Id: Ic7cbebe54a38af5b5c4639eb7641a20de6864a26
Merged-In: Ic7cbebe54a38af5b5c4639eb7641a20de6864a26
(cherry picked from commit 7182b0e3, aosp/1292438)