Added Sonic CLI commands to configure VxLAN ports

[aakashtiwari2630-max]

What I did

Added three new Sonic CLI commands to configure VxLAN ports:

1. configure vxlan destination-port
2. configure vxlan source-port
3. configure vxlan source-port-mask

After configuring these commands, SWITCH_TABLE in APP_DB will be updated dynamically so that the VxLAN port values are active for installed VxLAN tunnels.

Also, after configuring these commands, the port values will be stored in DEVICE_METADATA, so that in case of config reload or reboot, the same values are replayed using vxlanmgrd. Refer to:
sonic-net/sonic-swss#4492

Please note: After configuring these commands, config save is necessary for the port settings saved under DEVICE_METADATA to persist.

How I did it

How to verify it

Added 3 new tests.
tests/vxlan_test.py::TestVxlan::test_config_vxlan_destination_port PASSED [ 91%]
tests/vxlan_test.py::TestVxlan::test_config_vxlan_source_port PASSED [ 95%]
tests/vxlan_test.py::TestVxlan::test_config_vxlan_source_port_mask PASSED [100%]

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

root@sonic:/home/admin# config vxlan destination-port 51234
VXLAN destination port set to 51234
root@sonic:/home/admin# config vxlan source-port 1234
VXLAN source port set to 1234
root@sonic:/home/admin# config vxlan source-port-mask 7
VXLAN source port mask set to 7

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[prsunny]

I dont think DEVICE_METADATA is the right place to save this vxlan configs

[aakashtiwari2630-max]

I dont think DEVICE_METADATA is the right place to save this vxlan configs

I followed the example of other similar SWITCH_TABLE properties like ecmp_hash_offset and ecmp_hash_seed for this. But let me know if you can think of any other option.