[Thinkit] Update hard-coded dscp-to-queue mappings to match our configs, Configure switches sequentially with ConfigureSwitchPairAndReturnP4RuntimeSessionPair, Stop masking fixed bug, add helper methods for generating IPv6 and WCMP flows, Vlan tag test & gNMI port breakout tests.

[Thinkit] Update hard-coded dscp-to-queue mappings to match our configs, Configure switches sequentially with ConfigureSwitchPairAndReturnP4RuntimeSessionPair, Stop masking fixed bug, add helper methods for generating IPv6 and WCMP flows, Vlan tag test & gNMI port breakout tests. #4433