statement-distribution: Fix CostMinor("Unexpected Statement") (#3223)

On grid distribution messages have two paths of reaching a node, so
there is the possiblity of a race when two peers send each other the
same statement around the same time. Statement local_knowledge will tell
us that the peer should have not send the statement because we sent it
to it.

Fix it by also keeping track only of the statement we received from a
given peer and penalize it only if it sends it to us more than once.

Fixes: https://github.com/paritytech/polkadot-sdk/issues/2346



Additionally, also use different Cost labels for different paths to make
it easier to debug things.

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