Add test case as per @dgsudharsan

tests/test_portchannel.py

@@ -464,6 +464,51 @@ def test_portchannel_member_netdev_oper_status(self, dvs, testlog):
         # wait for port-channel deletion
         time.sleep(1)
 
+    # Make sure if a PortChannel member port tries to set an MTU that it is
+    # ignored and does not cause a runtime error.
+    def test_portchannel_member_mtu(self, dvs, testlog):
+        config_db = swsscommon.DBConnector(swsscommon.CONFIG_DB, dvs.redis_sock, 0)
+        app_db = swsscommon.DBConnector(swsscommon.APPL_DB, dvs.redis_sock, 0)
+
+        # create port-channel
+        tbl = swsscommon.Table(config_db, "PORTCHANNEL")
+        fvs = swsscommon.FieldValuePairs([("admin_status", "up"),("mtu", "9100"),("oper_status", "up")])
+        tbl.set("PortChannel111", fvs)
+
+        # set port-channel oper status
+        tbl = swsscommon.ProducerStateTable(app_db, "LAG_TABLE")
+        fvs = swsscommon.FieldValuePairs([("admin_status", "up"),("mtu", "9100"),("oper_status", "up")])
+        tbl.set("PortChannel111", fvs)
+
+        # add members to port-channel
+        tbl = swsscommon.Table(config_db, "PORTCHANNEL_MEMBER")
+        fvs = swsscommon.FieldValuePairs([("NULL", "NULL")])
+        tbl.set("PortChannel111|Ethernet0", fvs)
+        tbl.set("PortChannel111|Ethernet4", fvs)
+
+        # wait for port-channel netdev creation
+        time.sleep(1)
+
+        tbl = swsscommon.Table(config_db, "PORT")
+        fvs = swsscommon.FieldValuePairs([("mtu", "9100")])
+        tbl.set("Ethernet0", fvs)
+
+        # wait for attempted configuration to be applied
+        time.sleep(1)
+
+        # remove port-channel members
+        tbl = swsscommon.Table(config_db, "PORTCHANNEL_MEMBER")
+        tbl._del("PortChannel111|Ethernet0")
+        tbl._del("PortChannel111|Ethernet4")
+
+        # remove port-channel
+        tbl = swsscommon.Table(config_db, "PORTCHANNEL")
+        tbl._del("PortChannel111")
+
+        # wait for port-channel deletion
+        time.sleep(1)
+
+
 # Add Dummy always-pass test at end as workaroud
 # for issue when Flaky fail on final test it invokes module tear-down before retrying
 def test_nonflaky_dummy():