Add 'default' option for sFlow.

[venkatmahalingam]

Signed-off-by: Venkatesan Mahalingam [email protected]

The changes are copied from #845 to resolve the conflict.

The dependent swss PR : sonic-net/sonic-swss#1728

Adding the 'default' option to allow user to set an interface's
sFlow sampling-rate back to default.

• What I did
  Add a 'default' option so users can revert to the default sFlow sampling-rate on an interface.

• How I did it
  Updated the config script in config/main.py.

• How to verify it
  Unit-test:

root@sonic:~# show sflow interface | less

sFlow interface configurations
+-------------+---------------+-----------------+
| Interface   | Admin State   |   Sampling Rate |
+=============+===============+=================+
| Ethernet0   | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet4   | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet8   | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet12  | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet16  | up            |            4000 |
+-------------+---------------+-----------------+

root@sonic:~# config sflow interface sample-rate Ethernet0 222
Error: Sample rate must be between 256 and 8388608 or default
root@sonic:~# config sflow interface sample-rate Ethernet0 333
root@sonic:~# config sflow interface sample-rate Ethernet4 444
root@sonic:~# show sflow interface | less

sFlow interface configurations
+-------------+---------------+-----------------+
| Interface   | Admin State   |   Sampling Rate |
+=============+===============+=================+
| Ethernet0   | up            |             333 |
+-------------+---------------+-----------------+
| Ethernet4   | up            |             444 |
+-------------+---------------+-----------------+


root@sonic:~# config sflow interface sample-rate Ethernet0 default
root@sonic:~# config sflow interface sample-rate Ethernet4 default
root@sonic:~# config sflow interface sample-rate Ethernet8 default
root@sonic:~# show sflow interface | less

sFlow interface configurations
+-------------+---------------+-----------------+
| Interface   | Admin State   |   Sampling Rate |
+=============+===============+=================+
| Ethernet0   | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet4   | up            |            4000 |
+-------------+---------------+-----------------+
| Ethernet8   | up            |            4000 |
+-------------+---------------+-----------------+

Notice Ethernet0/4 has their sampling-rate restored to default (4000), but if I apply 'default' to a interface (Ethernet8) t

[prsunny]

Could you please add a unit test for default ?

[venkatmahalingam]

Could you please add a unit test for default ?

Done, please review the PR and merge if changes look good.