v2.0: rolls out chained Merkle shreds to ~21% of mainnet slots (backport of #4431) (#4434)

rolls out chained Merkle shreds to ~21% of mainnet slots (#4431)

(cherry picked from commit 9d09787d21da942f09751feebd0d67f4ee7a27a7)

Co-authored-by: behzad nouri <behzadnouri@gmail.com>

turbine/src/broadcast_stage/standard_broadcast_run.rs

@@ -510,8 +510,8 @@ fn should_chain_merkle_shreds(slot: Slot, cluster_type: ClusterType) -> bool {
     match cluster_type {
         ClusterType::Development => true,
         ClusterType::Devnet => true,
-        // Roll out chained Merkle shreds to ~5% of mainnet slots.
-        ClusterType::MainnetBeta => slot % 19 == 1,
+        // Roll out chained Merkle shreds to ~21% of mainnet slots.
+        ClusterType::MainnetBeta => slot % 19 < 4,
         ClusterType::Testnet => true,
     }
 }