Altair networking (#2300)

## Issue Addressed

Resolves #2278 

## Proposed Changes

Implements the networking components for the Altair hard fork https://github.com/ethereum/eth2.0-specs/blob/dev/specs/altair/p2p-interface.md

## Additional Info

This PR acts as the base branch for networking changes and tracks https://github.com/sigp/lighthouse/pull/2279 . Changes to gossip, rpc and discovery can be separate PRs to be merged here for ease of review.

Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/network/src/router/mod.rs

@@ -247,6 +247,31 @@ impl<T: BeaconChainTypes> Router<T> {
                 self.processor
                     .on_attester_slashing_gossip(id, peer_id, attester_slashing);
             }
+            PubsubMessage::SignedContributionAndProof(contribution_and_proof) => {
+                trace!(
+                    self.log,
+                    "Received sync committee aggregate";
+                    "peer_id" => %peer_id
+                );
+                self.processor.on_sync_committee_contribution_gossip(
+                    id,
+                    peer_id,
+                    *contribution_and_proof,
+                );
+            }
+            PubsubMessage::SyncCommitteeMessage(sync_committtee_msg) => {
+                trace!(
+                    self.log,
+                    "Received sync committee signature";
+                    "peer_id" => %peer_id
+                );
+                self.processor.on_sync_committee_signature_gossip(
+                    id,
+                    peer_id,
+                    sync_committtee_msg.1,
+                    sync_committtee_msg.0,
+                );
+            }
         }
     }
 }