Update sonic-swss submodule

639d10e (HEAD, origin/202012) [PFC_WD] [202012] Avoid applying ZeroBuffer Profiles to ingress PG when a PFC storm is detected (sonic-net#2310)
475ae19 [202012] [cherry-pick] Apply `DSCP_TO_TC_MAP` from `PORT_QOS_MAP|global` to switch level (sonic-net#2328)
aa6f855 [ci] Change artifact reference pipeline to common lib pipeline. (sonic-net#2294)
752f8c5 [ci] Use correct branch when downloading artifact. (sonic-net#2292)
b3fcc5d [ci] Improve azp trigger settings to automaticlly support new release branch. (sonic-net#2289)

Signed-off-by: Vivek Reddy <[email protected]>