Add unit test for PrivateDnsConfig

The unit test is added to ensure the conversion between PrivateDnsConfig
and PrivateDnsConfigParcel.

Bug: 240259333
Bug: 261404136
Test: atest NetworkStackTests:PrivateDnsConfigTest
Change-Id: I9a03d3b4c07fd3e15720c9fc3f47b3389c7ec029
1 file changed