Revert^2 "[ST02.2] Use the getters of DnsHeader"

Reason for revert: November mainline trains has been branched,
                   re-submit CLs and request API review.

Re-submitted Changes:
Ib5616c65c:[ST02.2] Use the getters of DnsHeader
I5e58f99b0:[ST02.1] Add TYPE_CNAME constant to DnsResolver
I0c1547cbc:[ST02] Add methods for synthesizing DNS packets

Change-Id: Ifb727e464d3523bd8dee0f2d919a8fb4a9d207c5