Fixing rootguard timeout issue for mst

Author: wajahatrazi

src/sonic-yang-models/tests/yang_model_tests/test_yang_model.py

@@ -263,12 +263,10 @@ def test_run_tests(self):
             for test in self.tests:
                 test = test.strip()
                 if test in self.ExceptionTests:
-                    ret = ret + self.runExceptionTest(test);
+                    ret = ret + self.runExceptionTest(test)
                 elif test in self.SpecialTests:
-                    ret = ret + self.runSpecialTest(test);
+                    ret = ret + self.runSpecialTest(test)
                 else:
-                    #log.error("Unexpected Test: {}".format(test))
-                    #ret = ret + 1
                     raise Exception("Unexpected Test")
         except Exception as e:
             ret = FAIL * len(self.tests)

src/sonic-yang-models/yang-models/sonic-spanning-tree.yang

@@ -151,6 +151,7 @@ module sonic-spanning-tree {
                     }
                     units "seconds";
                     default 30;
+                    when "../mode = 'pvst'";  // Only apply the default when mode is pvst
                     must "../mode != 'mst'" {
                         error-message "Root guard timeout is not allowed in MST mode.";
                         error-app-tag stp-invalid;