Log Message:
Updated net/ocaml-ipaddr to version 3.1.0.

Package is now compatible with dune 1.7.

Several backwards incompatible changes in version 3.0.0:
- sexp serialisers removed from main interface;
- macaddr module now in separate opam package;
- replace of_string/bytes functions with rresult types;
- use sexplib0 instead of the full sexp library;
- changes to function signatures.

Full details in the CHANGES.md file; there are also several minor changes.