When stopping the swss, pmon or bgp containers, log messages like the following can be seen:
```
Aug 23 22:50:43.789760 sonic-dut INFO swss#supervisord 2020-08-23 22:50:10,061 ERRO pool dependent-startup event buffer overflowed, discarding event 34
Aug 23 22:50:43.789760 sonic-dut INFO swss#supervisord 2020-08-23 22:50:10,063 ERRO pool dependent-startup event buffer overflowed, discarding event 35
Aug 23 22:50:43.789760 sonic-dut INFO swss#supervisord 2020-08-23 22:50:10,064 ERRO pool dependent-startup event buffer overflowed, discarding event 36
Aug 23 22:50:43.789760 sonic-dut INFO swss#supervisord 2020-08-23 22:50:10,066 ERRO pool dependent-startup event buffer overflowed, discarding event 37
```
This is due to the number of programs in the container managed by supervisor, all generating events at the same time. The default event queue buffer size in supervisor is 10. This patch increases that value in all containers in order to eliminate these errors. As more programs are added to the containers, we may need to further adjust these values. I increased all buffer sizes to 25 except for containers with more programs or templated supervisor.conf files which allow for a variable number of programs. In these cases I increased the buffer size to 50. One final exception is the swss container, where the buffer fills up to ~50, so I increased this buffer to 100.
Resolves https://github.com/Azure/sonic-buildimage/issues/5241
Introduce a new "sflow" container (if ENABLE_SFLOW is set). The new docker will include:
hsflowd : host-sflow based daemon is the sFlow agent
psample : Built from libpsample repository. Useful in debugging sampled packets/groups.
sflowtool : Locally dump sflow samples (e.g. with a in-unit collector)
In case of SONiC-VS, enable psample & act_sample kernel modules.
VS' syncd needs iproute2=4.20.0-2~bpo9+1 & libcap2-bin=1:2.25-1 to support tc-sample
tc-syncd is provided as a convenience tool for debugging (e.g. tc-syncd filter show ...)
