[Mempool] Increase the maximum concurrent task for bounded executor (#2390)

Author: sitalkedia

config/src/config/mempool_config.rs

@@ -29,7 +29,7 @@ impl Default for MempoolConfig {
             shared_mempool_backoff_interval_ms: 30_000,
             shared_mempool_batch_size: 100,
             shared_mempool_ack_timeout_ms: 2_000,
-            shared_mempool_max_concurrent_inbound_syncs: 2,
+            shared_mempool_max_concurrent_inbound_syncs: 4,
             max_broadcasts_per_peer: 1,
             mempool_snapshot_interval_secs: 180,
             capacity: 1_000_000,