Use parse() instead of _parse() in LogprofHeaderTest

The *LogprofHeaderTest accidently used the private _parse() insteaf of
the official parse().

utils/test/test-capability.py

@@ -451,7 +451,7 @@ class CapabilityLogprofHeaderTest(AATest):
     ]
 
     def _run_test(self, params, expected):
-        obj = CapabilityRule._parse(params)
+        obj = CapabilityRule.parse(params)
         self.assertEqual(obj.logprof_header(), expected)
 
 # --- tests for CapabilityRuleset --- #