datatransfer: fix peer certificate checks

Implementation based on dht::crypto::TrustList was not able
to remove the disconnected peer (API to do so doesn't exist).
Re-implement another system to check incoming TLS certificates.

Change-Id: I230775d22dde0b4b0a6768b7db3c94faef56634b
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>