R4R: fix metatx estimateGas

[wwqicode-blkchain]

if metatx not nil, sponsorAmount is set by gasCap(price), but should be similar to gasPrice * gasUsed. this causes estimateGas failed if gasUsed larger than 1.(100percent and 0 fromBalance)
e.g.: 100% sponsor, and msg.sender has no MNT. sponsorAmount will be set as feeCap. Balance in total is 0 + feeCap, and will also set to "avaliable". Then allowance is set by avaliable div feeCap, so allowance will be 1. If only the gasUsed larger than 1, error msg "gas required exceeds allowance (1)" will be returned.

[Tri-stone]

sponser & user's balance are added to available, but not all their balance are used to afford gasFee.

• in a case, sponser's balance is used to afford, and user's balance should not be involved.

[wwqicode-blkchain]

Because of we can not get the correct gasLimit before EstimateGas，we can only calculate sponsorAmount and selfAmount by kind of blockGasLimit feeCap * hi. The results of two amount may be much larger than balance. Such judgments may be inappropriate.

[abelliumnt]

sponsorAmount, selfAmount := types.CalculateSponsorPercentAmount(metaTxParams, new(big.Int).Mul(feeCap, new(big.Int).SetUint64(hi)))

available should be no less than selfAmount. Please add this check.

[wwqicode-blkchain]

sponsorAmount and selfAmount will be a large number because we get them by CalculateSponsorPercentAmount with input feeCap * hi. The hi is kind of blockGasLimit, a huge number.
Therefore, making judgments based on such results is inaccurate.

[wwqicode-blkchain]

calculate amount inside estimateGas function is merely to assign a value to "available" but can not verify whether the balance is sufficient.
Or whether we can estimateGas with payload without metatx prefix pureGasLimit，then add a const number to the gasLimit metaTxGasLimit.
CalculateSponsorPercentAmount use metaTxGasLimit as input, sponsorAmount & selfAmount can be more accurate. Checking the balance would also be more meaningful.