[202012][submodule] Update sonic-sairedis submodule

Update sonic-sairedis submodule pointer to include the following:
* 1d3720e Added Flex Counters support for tunnel counters (sonic-net#886) ([sonic-net#1120](sonic-net/sonic-sairedis#1120))
* 6469456 [lgtm] Add uuid library (sonic-net#1119) ([sonic-net#1126](sonic-net/sonic-sairedis#1126))

Signed-off-by: dgsudharsan <[email protected]>