disabling proposer reorg should set parent_threshold to u64 max

Author: eserilev

beacon_node/src/config.rs

@@ -748,7 +748,7 @@ pub fn get_config<E: EthSpec>(
 
     if cli_args.is_present("disable-proposer-reorgs") {
         client_config.chain.re_org_head_threshold = None;
-        client_config.chain.re_org_parent_threshold = None;
+        client_config.chain.re_org_parent_threshold = u64::MAX;
     } else {
         client_config.chain.re_org_head_threshold = Some(
             clap_utils::parse_optional(cli_args, "proposer-reorg-threshold")?