Distribute a PoV after seconding it (#1924)

We need to distribute the PoV after we have seconded it. Other nodes
that will receive our `Secondded` statement and want to validate the
candidate another time will request this PoV from us.

polkadot/node/collation-generation/src/lib.rs

@@ -318,7 +318,7 @@ fn erasure_root(
 ) -> crate::error::Result<Hash> {
 	let available_data = AvailableData {
 		validation_data: persisted_validation,
-		pov,
+		pov: Arc::new(pov),
 	};
 
 	let chunks = polkadot_erasure_coding::obtain_chunks_v1(n_validators, &available_data)?;