[202012][submodule] Update sonic-sairedis submodule

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

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