net/discovery: Do not propagate external addr with different peerIDs (#6380)

This PR ensures that external addresses with different PeerIDs are not
propagated to the higher layer of the network code.

While at it, this ensures that libp2p only adds the `/p2p/peerid` part
to the discovered address if it does not contain it already.

This is a followup from:
- https://github.com/paritytech/polkadot-sdk/pull/6298

cc @paritytech/networking

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Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Dmitry Markin <dmitry@markin.tech>