add parameterized test for the softfork guard and its behavior

[arvidn]

this adds a new test for the softfork guard, parameterized on mempool mode, the extension value passed in and flags. Since the BLS soft-fork has already activated, the flags parameter isn't so interesting. but it will be for the CHIP-34 patch.

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 9081205552

Details

• 28 of 28 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 94.162%

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Totals
Change from base Build 8986872347:	0.09%
Covered Lines:	5806
Relevant Lines:	6166

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💛 - Coveralls