Dtls12Server.decryptRecordPayload

const(ubyte)[] decryptRecordPayload(const(ubyte)[]  payload,
           DtlsRecordHeader header)

Decrypts an encrypted DTLS 1.2 record payload using the read AEAD.

Payload format: explicit_nonce (8) | ciphertext | tag (16), with the epoch and sequence number taken from the record header.

`payload`	The encrypted record payload.
`header`	The DTLS record header.

The decrypted plaintext, or null on failure.