MemoryDtlsTransport.recvFrom

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

Receive a single datagram.

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

Number of bytes received (>0), IoResult.WOULD_BLOCK if no data available,

IoResult.CLOSED if the transport is closed.