"invalid block" spam during state sync

[saketh-are]

The following error is printed repeatedly while a node is in state sync.

nearcore/chain/client/src/client_actor.rs

Line 2068 in cdb8055

error!(target: "client", ?err, ?block_hash, "Received an invalid block during state sync");

The spam occurs because the node receives the new blocks from the head of the chain which are too far ahead for it to validate.

Instead of validating all received blocks, we should print the error only if the node receives a block it cares about during state sync and is unable to validate it:

nearcore/chain/client/src/client_actor.rs

Lines 2046 to 2051 in cdb8055

	/// case of a node syncing its state it is looking for 2 specific blocks:
	/// * The first block of the new epoch
	/// * The last block of the prev epoch
	///
	/// Additionally if there were missing chunks in the blocks leading to the
	/// sync hash block we need to store extra blocks.