stats: support multiple works for error counters

The current code only allowed access to the main thread error counters.
That is not so useful for a multi worker instance.
No return a vector indexed by thread of counter_t values.

Type: fix

Change-Id: Ie322c8889c0c8175e1116e71de04a2cf453b9ed7
Signed-off-by: Ole Troan <ot@cisco.com>

test/framework.py

@@ -1027,6 +1027,11 @@ class VppTestCase(unittest.TestCase):
                     counter_value = int(results[0])
                     break
 
+    def assert_error_counter_equal(self, counter, expected_value):
+        counter_value = self.statistics.get_err_counter(counter)
+        self.assert_equal(counter_value, expected_value,
+                          "error counter `%s'" % counter)
+
     @classmethod
     def sleep(cls, timeout, remark=None):