Fix merge rpc length limits (#3133)

## Issue Addressed

N/A

## Proposed Changes

Fix the upper bound for blocks by root responses to be equal to the max merge block size instead of altair.
Further make the rpc response limits fork aware.

beacon_node/lighthouse_network/src/peer_manager/mod.rs

@@ -459,7 +459,7 @@ impl<TSpec: EthSpec> PeerManager<TSpec> {
                 // Our fault. Do nothing
                 return;
             }
-            RPCError::InvalidData => {
+            RPCError::InvalidData(_) => {
                 // Peer is not complying with the protocol. This is considered a malicious action
                 PeerAction::Fatal
             }