These were flagged by `cargo clippy`:
warning: you seem to be trying to use match for destructuring a
single pattern. Consider using `if let`
warning: called `.nth(0)` on a `std::iter::Iterator`, when `.next()`
is equivalent
warning: using `write!()` with a format string that ends in a single
newline
warning: useless conversion to the same type:
`smoltcp::wire::Ipv4Address`
warning: called `map(f)` on an `Option` value where `f` is a closure
that returns the unit type `()`
warning: returning the result of a `let` binding from a block
warning: use of `unwrap_or` followed by a function call
ea4579d68a