Simplify some pattern-matches (#16402)

When those match an exact combinator on Option / Result.

Tool-aided by [comby-rust](https://github.com/huitseeker/comby-rust).

net-utils/src/lib.rs

@@ -198,8 +198,7 @@ fn do_verify_reachable_ports(
                     .collect::<Vec<_>>(),
                 checked_ports_and_sockets
                     .iter()
-                    .map(|(_, sockets)| sockets)
-                    .flatten(),
+                    .flat_map(|(_, sockets)| sockets),
             );
 
             let _ = ip_echo_server_request(