Add a resolver option to enforce AID_DNS on query

The default behavior is that plaintext DNS queries are sent by the
application's UID using fchown(). DoT are sent with an UID of AID_DNS
This option control the plaintext uid of DNS query.

Bug: 154910763
Test: atest
Change-Id: Iada5d850d8bb9d7b0ad46f5c28a1fff22c7d11a6