[Mellanox] Fix issue: set lpmode by platform API does not work (#11732)

- Why I did it
Fix issue: set lpmode by platform API does not work

- How I did it
Fix miss return value in code

- How to verify it
Manual test

platform/mellanox/mlnx-platform-api/sonic_platform/sfp.py

@@ -53,6 +53,8 @@
         SX_PORT_MODULE_STATUS_UNPLUGGED = 2
         SX_PORT_MODULE_STATUS_PLUGGED_WITH_ERROR = 3
         SX_PORT_MODULE_STATUS_PLUGGED_DISABLED = 4
+        SX_PORT_ADMIN_STATUS_UP = True
+        SX_PORT_ADMIN_STATUS_DOWN = False
 except KeyError:
     pass
 
@@ -571,7 +573,7 @@ def _fetch_port_status(cls, sdk_handle, log_port):
     @classmethod
     def is_port_admin_status_up(cls, sdk_handle, log_port):
         _, admin_state = cls._fetch_port_status(sdk_handle, log_port);
-        admin_state == SX_PORT_ADMIN_STATUS_UP
+        return admin_state == SX_PORT_ADMIN_STATUS_UP
 
 
     @classmethod

platform/mellanox/mlnx-platform-api/tests/test_sfp.py

@@ -111,3 +111,11 @@ def test_sfp_read_eeprom(self):
         sfp = SFP(0)
         assert output_sfp.y_cable_part_number == sfp.read_eeprom(offset, 16).decode()
         MlxregManager.read_mlxred_eeprom.assert_called_with(132, 4, 16)
+
+    @mock.patch('sonic_platform.sfp.SFP._fetch_port_status')
+    def test_is_port_admin_status_up(self, mock_port_status):
+        mock_port_status.return_value = (0, True)
+        assert SFP.is_port_admin_status_up(None, None)
+
+        mock_port_status.return_value = (0, False)
+        assert not SFP.is_port_admin_status_up(None, None)