Use INodeAddress type in message handling

[ScottyPoi]

Fixes issue caused by #682 / #684

Message handling must use INodeAddress type, since onTalkRequest events from discv5 do not always contain an ENR.

All network message handlers were updated to use INodeAddress, which is all that is needed for sendTalkResponse.

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This gets a little tricky when a new uTP request is created. All uTP messages happen via talkReq, which requires an ENR to send. However, there are times when the uTP request needs to be instantiated before the peer's ENR has become available. So a new uTP request can be created using either INodeAddress or ENR. In cases where we use the INodeAddress, we optimistically hope that by the time we need to send the first uTP packet, the peer's ENR has become available.

[ScottyPoi]

note: the last commit 56dfc59, is a temporary patch for code that is currently getting refactored in a separate open PR.

[acolytec3]

LGTM