v1.16: rolls out merkle shreds to ~50% of mainnet slots (backport of #…

…32678) (#32720)

rolls out merkle shreds to ~50% of mainnet slots (#32678)

(cherry picked from commit 2078208)

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

core/src/broadcast_stage/standard_broadcast_run.rs

@@ -500,7 +500,7 @@ impl BroadcastRun for StandardBroadcastRun {
 fn should_use_merkle_variant(slot: Slot, cluster_type: ClusterType) -> bool {
     match cluster_type {
         ClusterType::Testnet | ClusterType::Devnet | ClusterType::Development => true,
-        ClusterType::MainnetBeta => (slot % 19) < 4,
+        ClusterType::MainnetBeta => (slot % 19) < 10,
     }
 }