PollDtlsTransport.recvFrom

ptrdiff_t recvFrom(ubyte[] buffer, out DatagramEndpoint sender)

Receives a single datagram from the socket.

`buffer`	Buffer to receive the datagram into.
`sender`	Output parameter set to the sender's address.

Bytes received (>0), IoResult.WOULD_BLOCK if no data

available, IoResult.ERROR on failure.