TxPool: Do not propagate transaction to the same peer

According to https://github.com/ethereum/devp2p/blob/master/caps/eth.md#transaction-exchange node shouldn't send transactions to the peer which already has it.

A few ways to solve it:
* remember which transactions have been sent to which peers
* on connect exchange pools content using [NewPooledTransactionHashes](https://github.com/ethereum/devp2p/blob/master/caps/eth.md#newpooledtransactionhashes-0x08) which will clearly shows which transactions the peer has.
* remember which inbound transactions if node received transaction for a peer it means this peer has this transaction