[202012][cherry-pick] Add two extra lossless queues for bounced back traffic

[bingwang-ms]

Why I did it

This PR is to cherry-pick #10496 into 202012 branch after resolving conflicts.

This PR is to add two extra lossless queues for bounced back traffic.
HLD sonic-net/SONiC#950

SKUs include

Arista-7050CX3-32S-C32
Arista-7050CX3-32S-D48C8
Arista-7260CX3-D108C8
Arista-7260CX3-C64
Arista-7260CX3-Q64

How I did it

Update the buffers.json.j2 template and buffers_config.j2 template to generate new BUFFER_QUEUE table.

• For T1 devices, queue 2 and queue 6 are set as lossless queues on T0 facing ports.
• For T0 devices, queue 2 and queue 6 are set as lossless queues on T1 facing ports.
• Queue 7 is added as a new lossy queue as DSCP 48 is mapped to TC 7, and then mapped into Queue 7

How to verify it

1. Verified by UT
2. Verified by coping the new template and generate buffer config with sonic-cfggen

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111

Description for the changelog

This PR is to add two extra lossless queues for bounced back traffic.

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[bingwang-ms]

vstest will pass after PR #10608 is merged as the required sample minigraph files are checked-in in that PR.

/sonic/src/sonic-config-engine$ python3 setup.py test 
......
----------------------------------------------------------------------
Ran 169 tests in 52.774s

OK

[stephenxs]

@bingwang-ms can you resolve the conflict and retrigger the build? thanks.

[stephenxs]

@bingwang-ms could you please fix the conflicts? thanks