DAL: Reconsider ordering of checks in `validate_attestation`

Follow-up from !7140 (comment 1212416401)

Currently, the checks in validate_attestation is done in the following order:

1. Attestation size check.
2. Attestation level check.
3. Attestation membership check.

But we are not sure if this order is the ideal ordering.

We should confirm whether it is problematic and fix the ordering if neccessary.