Respect gas limit config in eth_gasPrice endpoint

[DarianShawn]

Description

The PR uses gas limit as the basic gas price in the eth_gasPrice endpoint.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

[codecov-commenter]

Codecov Report

Merging #170 (d5eacff) into dev (e56d55f) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #170      +/-   ##
==========================================
- Coverage   51.43%   51.39%   -0.05%     
==========================================
  Files         113      113              
  Lines       16830    16839       +9     
==========================================
- Hits         8657     8654       -3     
- Misses       7436     7446      +10     
- Partials      737      739       +2     

Impacted Files	Coverage Δ
jsonrpc/dispatcher.go	54.72% <100.00%> (+1.05%)	⬆️
jsonrpc/eth_endpoint.go	71.36% <100.00%> (-0.19%)	⬇️
jsonrpc/jsonrpc.go	19.67% <100.00%> (+2.72%)	⬆️
network/server_discovery.go	73.88% <0.00%> (-7.65%)	⬇️

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[abrahamcruise321]

lgtm.