Do not penalize peers on execution layer offline errors (#3258)

## Issue Addressed

Partly resolves https://github.com/sigp/lighthouse/issues/3032

## Proposed Changes

Extracts some of the functionality of #3094 into a separate PR as the original PR requires a bit more work.
Do not unnecessarily penalize peers when we fail to validate received execution payloads because our execution layer is offline.

beacon_node/network/src/sync/backfill_sync/mod.rs

@@ -8,7 +8,7 @@
 //! If a batch fails, the backfill sync cannot progress. In this scenario, we mark the backfill
 //! sync as failed, log an error and attempt to retry once a new peer joins the node.
 
-use crate::beacon_processor::{ChainSegmentProcessId, WorkEvent as BeaconWorkEvent};
+use crate::beacon_processor::{ChainSegmentProcessId, FailureMode, WorkEvent as BeaconWorkEvent};
 use crate::sync::manager::{BatchProcessResult, Id};
 use crate::sync::network_context::SyncNetworkContext;
 use crate::sync::range_sync::{BatchConfig, BatchId, BatchInfo, BatchProcessingResult, BatchState};
@@ -554,6 +554,7 @@ impl<T: BeaconChainTypes> BackFillSync<T> {
                     imported_blocks: false,
                     // The beacon processor queue is full, no need to penalize the peer.
                     peer_action: None,
+                    mode: FailureMode::ConsensusLayer,
                 },
             )
         } else {
@@ -638,6 +639,7 @@ impl<T: BeaconChainTypes> BackFillSync<T> {
             BatchProcessResult::Failed {
                 imported_blocks,
                 peer_action,
+                mode: _,
             } => {
                 let batch = match self.batches.get_mut(&batch_id) {
                     Some(v) => v,