Fix error when running 'show lldp table' or 'show lldp neighbor'
through SSH command. (sonic-net#1067)
[201911]: Multi asic show interface support (sonic-net#1070)
[counterpoll] Add new FC group for port buffer drop counters
(sonic-net#1024)
[201911] show interface portchannel support for Multi ASIC
(sonic-net#1071)
Fix a typo in mellanox_buffer_migrator (sonic-net#1090)
Fix pfcwd stats crash with invalid queue name (sonic-net#1077)
[PFCWD] Fix issue with "pfcwd show stats" command during SONiC init
(sonic-net#1018)
enable watchdog before running platform specific reboot plugin
(sonic-net#1037)
Add namespace of the process in the coredump filename. (sonic-net#1091)

When updating `green_min_threshold`, `green_max_threshold`, or
`green_drop_probability` in WRED profiles for which `wred_green_enable`
is false (or not set) using the `apply-patch` command, sometimes we see
these errors:
```
ERR syncd#syncd: [none] SAI_API_PORT:_brcm_sai_cosq_gport_discard_set:6205 cosq gport discard set failed with error Invalid parameter (0xfffffffc)
ERR syncd#syncd: [none] SAI_API_QUEUE:_brcm_sai_qos_queue_wred_set:1760 sai cosq gport discard set failed with error -5.
ERR syncd#syncd: [none] SAI_API_WRED:_brcm_xgs_sai_reapply_wred_profile:882 Apply queue config failed with error -5.
```
This PR fixes this issue by modifying `test_ecn_config_update.py` to not
generate JSON patches for WRED profiles for which `wred_green_enable` is
false (or not set). After this fix, these tests passed on a device on
which the same tests failed before the fix:
```
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_min_threshold] PASSED                                         [ 25%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_max_threshold] PASSED                                         [ 50%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_drop_probability] PASSED                                      [ 75%]
generic_config_updater/test_ecn_config_update.py::test_ecn_config_updates[replace-green_min_threshold,green_max_threshold,green_drop_probability] PASSED [100%]
```

Signed-off-by: Mahdi Ramezani <mramezani@microsoft.com>