Why I did it
This PR is to backport #11569 into 202012 branch.
This PR is to apply different DSCP_TO_TC_MAP to downlink and uplink ports on T1 in dualtor deployment.
For T1 downlink ports (To T0)
The DSCP_TO_TC_MAP is not changed. DSCP2 and DSCP6 are mapped to TC2 and TC6 respectively.
For T1 uplink ports (To T1)
A new DSCP_TO_TC_MAP|AZURE_UPLINK is defined and applied. DSCP2 and DSCP6 are mapped to TC1 to avoid mixing up lossy and lossless traffic from T2.
The extra lossy PG2 and PG6 added in PR #11157 is reverted as well because no traffic from T2 is mapped to PG2 or PG6 now.
How I did it
Define a new map DSCP_TO_TC_MAP|AZURE_UPLINK for 7260 T1.
How to verify it
Verified by test case in test_j2files.py.
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