Fix issue that dynamic/static threshold 0 can not be configured using mmuconfig (sonic-net#4049)

What I did
Fix issue that dynamic/static threshold 0 can not be configured using mmuconfig

Author: stephenxs

scripts/mmuconfig

@@ -196,9 +196,9 @@ def main(show_config, profile, alpha, staticth, trim, namespace, verbose):
             mmu_cfg.list()
         # Buffershow cannot modify profiles
         elif config and profile:
-            if alpha:
+            if alpha is not None:
                 mmu_cfg.set(profile, DYNAMIC_THRESHOLD, alpha)
-            elif staticth:
+            elif staticth is not None:
                 mmu_cfg.set(profile, STATIC_THRESHOLD, staticth)
             elif trim:
                 mmu_cfg.set(profile, PACKET_TRIMMING, trim)

tests/mmuconfig_input/mmuconfig_test_vectors.py

@@ -269,13 +269,30 @@
                                    'cmp_args': [',ingress_lossless_profile_hbm,static_th,12121213'],
                                    'rc_msg': ''
                                    },
-             'mmu_cfg_alpha' :    {'cmd' : ['config'],
-                                   'args' : ['-p', 'alpha_profile', '-a', '2'],
-                                   'rc' : 0,
-                                   'db_table' : 'BUFFER_PROFILE',
-                                   'cmp_args': [',alpha_profile,dynamic_th,2'],
-                                   'rc_msg' : ''
-                                  },
+             'mmu_cfg_static_th_zero': {
+                'cmd': ['config'],
+                'args': ['-p', 'ingress_lossless_profile_hbm', '-s', '0'],
+                'rc': 0,
+                'db_table': 'BUFFER_PROFILE',
+                'cmp_args': [',ingress_lossless_profile_hbm,static_th,0'],
+                'rc_msg': ''
+             },
+             'mmu_cfg_alpha': {
+               'cmd': ['config'],
+               'args': ['-p', 'alpha_profile', '-a', '2'],
+               'rc': 0,
+               'db_table': 'BUFFER_PROFILE',
+               'cmp_args': [',alpha_profile,dynamic_th,2'],
+               'rc_msg': ''
+             },
+             'mmu_cfg_alpha_zero': {
+                'cmd': ['config'],
+                'args': ['-p', 'alpha_profile', '-a', '0'],
+                'rc': 0,
+                'db_table': 'BUFFER_PROFILE',
+                'cmp_args': [',alpha_profile,dynamic_th,0'],
+                'rc_msg': ''
+             },
              'mmu_cfg_alpha_invalid': {'cmd': ['config'],
                                        'args': ['-p', 'alpha_profile', '-a', '12'],
                                        'rc': 2,

tests/mmuconfig_test.py

@@ -87,6 +87,12 @@ def test_mmu_alpha_invalid_config(self):
     def test_mmu_staticth_config(self):
         self.executor(testData['mmu_cfg_static_th'])
 
+    def test_mmu_alpha_zero_config(self):
+        self.executor(testData['mmu_cfg_alpha_zero'])
+
+    def test_mmu_staticth_zero_config(self):
+        self.executor(testData['mmu_cfg_static_th_zero'])
+
     def test_mmu_trim_config(self):
         self.executor(testData['mmu_cfg_trim'])