Update exitcode from invalidSyscall to illegalInstruction

[mininny]

Description
Change the revert code for reserved/invalid instruction encoding from InvalidSyscall to IllegalInstruction.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 60.92%. Comparing base (f01251b) to head (740e8f3).

Files with missing lines	Patch %	Lines
rvgo/fast/vm.go	0.00%	3 Missing ⚠️
rvgo/slow/vm.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           feature/mininny/audit-22     #134   +/-   ##
=========================================================
  Coverage                     60.92%   60.92%           
=========================================================
  Files                            27       27           
  Lines                          4195     4195           
=========================================================
  Hits                           2556     2556           
  Misses                         1492     1492           
  Partials                        147      147           

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