Run rustfmt on routing/mod.rs/re-enable it on the routing mod

In d257b8a we dropped our old
`rustfmt` per-file exclusion logic and replaced it with
`rustfmt_skip` tags in each previously-skipped files. This had the
unintended consequence of fully disabling `rustfmt` across the
`lightning` crate:

`rustfmt` operates recursively across files in any module it is
told to format. Previously, because we were running `rustfmt` on
each non-excluded file, this meant we wanted to exclude `mod.rs`
and `lib.rs` files - not doing so would result in the entire
module/crate being formatted. However, `cargo fmt --check` only
runs `rustfmt` once - on `lib.rs`. Because we added a top-level
`rustfmt_skip` in `lib.rs` this caused `rustfmt` to ignore it and
all modules.

Here we prepare to fix this by formatting
`lightning/src/routing/mod.rs`.

Author: TheBlueMatt

lightning/src/routing/mod.rs

@@ -1,5 +1,3 @@
-#![cfg_attr(rustfmt, rustfmt_skip)]
-
 // This file is Copyright its original authors, visible in version control
 // history.
 //
@@ -11,10 +9,10 @@
 
 //! Structs and impls for receiving messages about the network and storing the topology live here.
 
-pub mod utxo;
 pub mod gossip;
+mod log_approx;
 pub mod router;
 pub mod scoring;
-mod log_approx;
 #[cfg(test)]
 pub(crate) mod test_utils;
+pub mod utxo;