Filter port invalid MTU configuration (sonic-net#2378)

What I did
Filter port invalid MTU configuration
Adjust the MTU value to the range of [68,9216]

Author: pettershao-ragilenetworks

config/main.py

@@ -4212,7 +4212,7 @@ def _get_all_mgmtinterface_keys():
 @interface.command()
 @click.pass_context
 @click.argument('interface_name', metavar='<interface_name>', required=True)
-@click.argument('interface_mtu', metavar='<interface_mtu>', required=True)
+@click.argument('interface_mtu', metavar='<interface_mtu>', required=True, type=click.IntRange(68, 9216))
 @click.option('-v', '--verbose', is_flag=True, help="Enable verbose output")
 def mtu(ctx, interface_name, interface_mtu, verbose):
     """Set interface mtu"""

tests/config_int_mtu_test.py

@@ -0,0 +1,26 @@
+import pytest
+import config.main as config
+from click.testing import CliRunner
+from utilities_common.db import Db
+
+class TestConfigInterfaceMtu(object):
+    def test_interface_mtu_check(self):
+        runner = CliRunner()
+        db = Db()
+        result = runner.invoke(config.config.commands["interface"].commands["mtu"],
+            ["Ethernet0", "68"], obj=db)
+        assert result.exit_code != 0
+
+        result1 = runner.invoke(config.config.commands["interface"].commands["mtu"],
+            ["Ethernet0", "9216"], obj=db)
+        assert result1.exit_code != 0
+
+    def test_interface_invalid_mtu_check(self):
+        runner = CliRunner()
+        db = Db()
+        result = runner.invoke(config.config.commands["interface"].commands["mtu"],
+            ["Ethernet0", "67"], obj=db)
+        assert "Error: Invalid value" in result.output
+        result1 = runner.invoke(config.config.commands["interface"].commands["mtu"],
+            ["Ethernet0", "9217"], obj=db)
+        assert "Error: Invalid value" in result1.output