lib/compare.rb: resolve rubocop Naming/AccessorMethodName issue

[rli9]

Reproduce

lkp-tests$ rubocop lib/compare.rb

lib/compare.rb:171:9: C: Naming/AccessorMethodName: Do not prefix writer method names with set_.
    def set_params(params)
        ^^^^^^^^^^
lib/compare.rb:393:9: C: Naming/AccessorMethodName: Do not prefix reader method names with get_.
    def get_all_stat_keys
        ^^^^^^^^^^^^^^^^^
lib/compare.rb:431:9: C: Naming/AccessorMethodName: Do not prefix reader method names with get_.
    def get_include_stat_keys
        ^^^^^^^^^^^^^^^^^^^^^
lib/compare.rb:456:9: C: Naming/AccessorMethodName: Do not prefix reader method names with get_.
    def get_include_all_failure_stat_keys
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/compare.rb:469:9: C: Naming/AccessorMethodName: Do not prefix reader method names with get_.
    def get_testcase_stat_keys
        ^^^^^^^^^^^^^^^^^^^^^^
lib/compare.rb:659:11: C: Naming/AccessorMethodName: Do not prefix writer method names with set_.
      def set_data_type(dt)
          ^^^^^^^^^^^^^

1 file inspected, 6 offenses detected

Reference
https://github.com/intel/lkp-tests/wiki/Coding-Standard#rubocop

Note
Besides the fix of rubocop issue, it is required to update the caller side to use new API