Add bypass private DNS test case and null network test for DnsResolver cts

1. add test case for testing bypass Private DNS
2. add null network test
3. minor change for cleanup

Bug: 130594022
Test: atest DnsResolverTest
Change-Id: I2da65fc1267a1975e014c0aafe2ae47df075b712
1 file changed
tree: d4771cd87c57ef8866d2b99f7cc97ef9e2907c21
  1. tests/