Add private DNS settings comparison in PrivateDnsConfig

This change adds a new method in PrivateDnsConfig to compare
whether two PrivateDnsConfigs have the mode and the hostname.

Bug: 240259333
Test: PrivateDnsConfigTest and DdrTrackerTest passed
Change-Id: I858ab3106247650c23dd9ef9db60770101bb07c8
3 files changed