Merge branch 'mlxsw-Test-coverage-for-DSCP-leftover-fix'

Petr Machata says:

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mlxsw: Test coverage for DSCP leftover fix

This patch set fixes some global scope pollution issues in the DSCP tests
(in patch #1), and then proceeds (in patch #2) to add a new test for
checking whether, after DSCP prioritization rules are removed from a port,
DSCP rewrites consistently to zero, instead of the last removed rule still
staying in effect.
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Signed-off-by: David S. Miller <davem@davemloft.net>