Inform DNS resolver whether DDR is enabled.

This is needed to cleanly flag on/off DDR and to ensure that
when it is flagged on, DnsResolver ignores the hardcoded list of
DoH providers and only uses DDR.

Bug: 240259333
Test: updated existing tests
Change-Id: I84c103a5a4d18294b6a4cc3301d0037d1a6673a4
2 files changed