EthernetTetheringTest: testTetherUdpV4Dns

Add a tethering IPv4 DNS test.

DNS query:
tethered device --> downstream --> dnsmasq forwarding --> upstream --> DNS server

DNS reply:
DNS server --> upstream --> dnsmasq forwarding --> downstream --> tethered device

Bug: 237369591
Test: atest EthernetTetheringTest
Change-Id: I2baa9d7ccf55d117f644c80e867fb8272f7daac5
2 files changed