The functionality is available through `Multiaddr::replace`.
What we currently call "nat_traversal" is merley a replacement of an IP
address prefix in a `Multiaddr`, hence it can be done directly on
`Multiaddr` values instead of having to go through a `Transport`.
In addition this PR consolidates changes made to `Multiaddr` in
previous commits which resulted in lots of deprecations. It adds some
more (see below for the complete list of API changes) and removes all
deprecated functionality, requiring a minor version bump.
Here are the changes to `multiaddr` compared to the currently published
version:
1. Removed `into_bytes` (use `to_vec` instead).
2. Renamed `to_bytes` to `to_vec`.
3. Removed `from_bytes` (use the `TryFrom` impl instead).
4. Added `with_capacity`.
5. Added `len`.
6. Removed `as_slice` (use `AsRef` impl instead).
7. Removed `encapsulate` (use `push` or `with` instead).
8. Removed `decapsulate` (use `pop` instead).
9. Renamed `append` to `push`.
10. Added `with`.
11. Added `replace`.
12. Removed `ToMultiaddr` trait (use `TryFrom` instead).
