Fix transaction route

[Qiao-Jin]

Summary or problem description
This is an issue similar to #1667. Currently incoming transactions will be handled in the following steps:

(1) Deserialized by RemoteNode

(2) Sent to Blockchain, check whether it's within mempool

(3) Sent to TransactionRouter to check witness

(4) Sent to Blockchain again to check fee, whether it's within mempool, and added to mempool

There are 2 porblems:

(1) There is a circled stream from step (2) to (4). Blockchain is called twice which would cause TPS drop.

(2) Func ContainsTransaction is called twice for a single transaction in step (2) and (4)

Do you have any solution you want to propose?

A new scenario for incoming transactions:

(1) Deserialized by RemoteNode

(2) Sent to TransactionRouter to check witness

(3) Sent to Blockchain to check fee, whether it's within mempool, and added to mempool

Neo Version

• Neo 3