[Mega Tracking] Align Prysm to Interop Networking Spec

[prestonvanloon]

The new interop networking spec has been merged (https://github.com/ethereum/eth2.0-specs/pull/1328).

Spec requirements

Interop requirements:

• [x] Support libp2p TCP transport for inbound/outbound IPv4 and IPv6 addresses.
• [x] Expose at least one IPv4 endpoint. #3211
• [x] All endpoints must be publicly dialable (no advertising local networked addresses or relay)
• [x] Testnet infrastructure configured to enable direct, inbound traffic
• [x] SecIO w/ secp256k1 for identity
• [x] mplex protocol for multiplexing
• [x] (optional) yamux protocol for multiplexing
• [x] Gossipsub alignment
• [x] RPC (req/res) alignment
• [x] Discovery (discv5) alignment

Mainnet requirements:

• [x] Noise handshakes (Moved to #3687)

Code changes

Not in any particular order. See networking design doc.

Migration:

• [x] Move/prefix sync and p2p packages with deprecated- as part of the migration. #3190 #3191
• [x] Mark existing p2p pb messages as deprecated #3194
• [x] Mark existing topic mappings as deprecated #3192 #3194

p2p package:

• [x] Add new p2p package with boilerplate libp2p configuration #3196
• [x] Add unit tests and explicit config to ensure libp2p configuration parameters meet the network spec requirements #3200

p2p encoding:

• [x] Add API for encoding registration
• [x] Register ssz encoder/decoder #3198 #3210
• [x] Register ssz_snappy encoder/decoder #3198 #3210
• [x] Add encoding enum flag for selecting the p2p encoding #3256
• [x] Prefix ssz encoded data with protobuf.Varint length indicator #3210

p2p hello/goodbye:

• [x] Add peerstore abstraction for tracking handshake responses
• [x] Add handler for hello #3216
• [x] Add handler for goodbye #3282

Initial sync:

• [x] Add round robin sync strategy
• [x] Add logic to sync round robin up to finalized epoch
• [x] Add logic to sync to head after finalized epoch

Topic mappings:

• [x] Add new message topic mappings #3201

Regular sync RPC:

• [x] /eth2/beacon_chain/req/beacon_blocks/1/{ssz,ssz_snappy} handler #3218
• [x] /eth2/beacon_chain/req/recent_beacon_blocks/1/{ssz,ssz_snappy} handler #3281
• [x] /eth2/beacon_chain/req/hello/1/{ssz,ssz_snappy} handler #3216
• [x] /eth2/beacon_chain/req/goodbye/1/{ssz,ssz_snappy} handler #3282
• [x] Add new message types #3199

Regular sync gossip sub:

• [x] /eth2/beacon_block/{ssz,ssz_snappy} handler & validator #3220
• [x] /eth2/beacon_attestation/{ssz,ssz_snappy} handler & validator
• [x] /eth2/voluntary_exit/{ssz,ssz_snappy} handler & validator #3227
• [x] /eth2/proposer_slashing/{ssz,ssz_snappy} handler & validator
• [x] /eth2/attester_slashing/{ssz,ssz_snappy} handler & validator

Broadcaster:

• [x] Broadcast with encoding #3226

Fork choice:

• [x] Add ReceiveBlock path that does not apply fork choice (for initial sync up to finalized epoch)

Discovery:

• [x] Change bootnode to use Discv5 instead of kademlia #3203
• [x] Allow node discovery via Discv5. #3211 - [ ] Handle topic search for stored node records. - [ ] Standardize interfaces to match libp2p for discovery and peer routing
• [x] ENR for nodes in prysm must conform with the required fields as stated here

Ssz:

• [x] Add support for proto enum fields (int32) https://github.com/prysmaticlabs/go-ssz/issues/66

[terencechain]

Interested in gossips and rpc alignments

[nisdas]

interested in discovery and RPC alingment