Make gasprice opcode return 0 for eth_call's with a zero gas price

[rachel-bousfield]

Makes the gasprice opcode return the actual amount paid by the user

[codecov]

Codecov Report

Merging #799 (45b6d29) into master (ff93280) will decrease coverage by 0.13%.
The diff coverage is 12.50%.

❗ Current head 45b6d29 differs from pull request most recent head 2282289. Consider uploading reports for the commit 2282289 to get more accurate results

@@            Coverage Diff             @@
##           master     #799      +/-   ##
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- Coverage   48.73%   48.59%   -0.14%     
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  Files         211      211              
  Lines       22939    22943       +4     
  Branches      494      494              
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- Hits        11180    11150      -30     
- Misses      10232    10261      +29     
- Partials     1527     1532       +5     

[fredlacs]

I think it would be best if gasprice surfaced was actually the basefee, when eth_call is set to zero gas price.
But that would diverge from geth (although I think geth would be better with the above behaviour)

That said, this change LGTM

[PlasmaPower]

LGTM - we'll revert this if as upstream geth accepts Fred's PR

[rachel-bousfield]

Here's Fred's upstream issue

• gasprice value in eth_call and eth_estimateGas ethereum/go-ethereum#25322