Validates the payload received from the other participant during round 2.
Note that this DOES NOT detect a non-common password. The only indication of a non-common password is through derivation of different keys (which can be detected explicitly by executing round 3 and round 4)
Must be called prior to {@link #calculateKeyingMaterial()}.
After execution, the {@link #getState() state} will be {@link #STATE_ROUND_2_VALIDATED}.
@throws CryptoException if validation fails.
@throws IllegalStateException if called prior to {@link #validateRound1PayloadReceived(JPAKERound1Payload)}, or multiple times