rust/clippy: allow result_unit_err in http2 only

Its the only module making use of this pattern, but we shouldn't let
new modules use this pattern.

rust/src/http2/mod.rs

@@ -15,6 +15,8 @@
  * 02110-1301, USA.
  */
 
+#![allow(clippy::result_unit_err)]
+
 mod decompression;
 pub mod detect;
 pub mod http2;

rust/src/lib.rs

@@ -29,7 +29,6 @@
 // To be fixed, but remove the noise for now.
 #![allow(clippy::match_like_matches_macro)]
 #![allow(clippy::module_inception)]
-#![allow(clippy::result_unit_err)]
 #![allow(clippy::type_complexity)]
 
 #[macro_use]