Make resetting implicit in TransportDeserializer::Read()

Summary:
Partial backport 6/7 of core PR16202:
https://github.com/bitcoin/bitcoin/pull/16202/commits/f342a5e61a73e1edf389b662d265d20cf26a1d51

Depends on D8226.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK, jasonbcox

Reviewed By: #bitcoin_abc, PiRK, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D8227