- Provides `pub async fn wait_recv_ready(&self) -> ()` and `pub fn poll_recv_ready(&self, cx: &mut Context<'_>) -> Poll<()>`.
This allows polling / waiting on a socket until it can be read, without dequeuing any packets.
- Provides `pub async fn wait_send_ready(&self) -> ()` and `pub fn poll_send_ready(&self, cx: &mut Context<'_> -> Poll<()>`
This allows polling / waiting on a socket until it becomes writable.
Added recv_from_with and send_to_with. These are conceptually similar
to TCP's read_with and write_with functions.
An application can parse received datagrams directly out of the
receive buffer or assemble a datagram of known-length directly into
the send buffer.
This is a breaking change for users of the poll_ functions. (Some might
not notice if they already pass in an IpEndpoint into poll_send_to, or
discard that item in poll_recv_from).
The "must not be called reentrantly" invariant is too "global" to
maintain comfortably, and the cost of the RefCell is negligible,
so this was a case of premature optimization.
