apply `Eth.Miner.GasCeil` to TxPool even the node did not enable `--mine` option
Otherwise, there could be accmulated pending transactions in txpool.
Take an example:
- Currently, BSC testnet's block gaslimit is 70M, as 20M gas is reserved for
SystemTxs, the maximum acceptable GasLimit for transaction is 50M.
- TxPool recevied a transaction with GasLimit 60M, it would be accepted in TxPool but it
will never be accepted by validators. Such kinds of transactions will be kept in txpool
and gradually make the txpool overflowed
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