Expose config max-round-blocks-to-import (#9439)

* Expose config max-round-blocks-to-import

* Fix test

ethcore/src/client/client.rs

@@ -262,13 +262,12 @@ impl Importer {
 
 	/// This is triggered by a message coming from a block queue when the block is ready for insertion
 	pub fn import_verified_blocks(&self, client: &Client) -> usize {
-
 		// Shortcut out if we know we're incapable of syncing the chain.
 		if !client.enabled.load(AtomicOrdering::Relaxed) {
 			return 0;
 		}
 
-		let max_blocks_to_import = 4;
+		let max_blocks_to_import = client.config.max_round_blocks_to_import;
 		let (imported_blocks, import_results, invalid_blocks, imported, proposed_blocks, duration, is_empty) = {
 			let mut imported_blocks = Vec::with_capacity(max_blocks_to_import);
 			let mut invalid_blocks = HashSet::new();

ethcore/src/client/config.rs

@@ -121,6 +121,8 @@ pub struct ClientConfig {
 	pub check_seal: bool,
 	/// Maximal number of transactions queued for verification in a separate thread.
 	pub transaction_verification_queue_size: usize,
+	/// Maximal number of blocks to import at each round.
+	pub max_round_blocks_to_import: usize,
 	/// Snapshot configuration
 	pub snapshot: SnapshotConfiguration,
 }
@@ -147,6 +149,7 @@ impl Default for ClientConfig {
 			history_mem: 32 * mb,
 			check_seal: true,
 			transaction_verification_queue_size: 8192,
+			max_round_blocks_to_import: 12,
 			snapshot: Default::default(),
 		}
 	}