substrate: peer_store: log warn on disconnecting because of reputation (#1299)

* substrate: peer_store: log error on disconnecting because of reputation

Disconnecting and banning a peer because of negative reputation is
usually an indicative of one of two things:
1. We've got a bug that forces disconnects.
2. We've got malicious peers that try to attack us.

We both cases I don't think we should hide this behind a trace log
and we should log errors, so that things are easy to notice and
debug/mitigated.

Signed-off-by: Alexandru Gheorghe <[email protected]>

* Move from error to warn

Signed-off-by: Alexandru Gheorghe <[email protected]>

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Signed-off-by: Alexandru Gheorghe <[email protected]>