Slightly increase some syncer defaults (#4679)

This is a partial revert of PR #4670.

zebrad/src/components/sync.rs

@@ -81,7 +81,7 @@ pub const MIN_LOOKAHEAD_LIMIT: usize = zebra_consensus::MAX_CHECKPOINT_HEIGHT_GA
 /// See [`MIN_LOOKAHEAD_LIMIT`] for details.
 ///
 /// TODO: increase to `MAX_CHECKPOINT_HEIGHT_GAP * 5`, after we implement orchard batching
-pub const DEFAULT_LOOKAHEAD_LIMIT: usize = MIN_LOOKAHEAD_LIMIT;
+pub const DEFAULT_LOOKAHEAD_LIMIT: usize = zebra_consensus::MAX_CHECKPOINT_HEIGHT_GAP * 3;
 
 /// The expected maximum number of hashes in an ObtainTips or ExtendTips response.
 ///

zebrad/src/config.rs

@@ -198,7 +198,7 @@ impl Default for SyncSection {
     fn default() -> Self {
         Self {
             // TODO: increase to 50, after we implement orchard batching
-            max_concurrent_block_requests: 25,
+            max_concurrent_block_requests: 40,
             lookahead_limit: sync::DEFAULT_LOOKAHEAD_LIMIT,
         }
     }