`T` always was the same as `Self`.
Also do a major bump on depending crates.

… in implementations (apart from Debug)

- where clauses are almost never needed on type definitions unless you
  need them in the `Drop` implementation
- Debug trait might be useful if (debug) logging gets added
- Clone/PartialEq/Eq shouldn't be needed ever in the implementations

1. get rid of "workaround-audit-bug" "feature"

2. no longer use tokio_util::codec::{Decoder, Encoder}

tokio_util::codec is "designed" for bytestreams (and building "frames"
of messages on top), but we need to deal with datagrams (which still
can contain multiples messages, just not one message across multiple
datagrams).

This make it a little less "combinable", but we actually don't want
people to reuse these codecs on bytestream (and writing an adapter
wouldn't be that hard anyway).

Also we can use a fixed error type, making dealing with it a little
bit easier.

Creating &mut [u8] (and &[u8]) for unitialized memory is undefined
behaviour even when not actually reading the data.

Use bytes::BufMut instead, and advance buffer in recv functions.
High level functions (without flags param) don't need to return length
of read, as it was used to advance the buffer - only low-level read
might return larger length than the buffer (PEEK + TRUNC flags).

This also bumps netlink-sys; the other crates already got bumped.

Preparation to make tokio and smol feature non-conflicting in
netlink-proto.

- This adds a new type paramater to connection for the socket being used.
- can drop tokio/smol selection from netlink-packet-audit