[Submodule update] sonic-sairedis

d821bc0 (HEAD -> master, origin/master, origin/HEAD) [Mellanox] Add SAI template config support (sonic-net#803)
bb341e9 [syncd] Bring back TimerWatchdog (sonic-net#821)
badf6ce Update .gitignore (sonic-net#822)
1494bc6 [meta] Mark local function static (sonic-net#818)
34e961c [pyext] Fix pyext/py2 library (sonic-net#820)
0d3749d Moved SAI Header to git tag v1.8.1 (sonic-net#816)
70fff78 Added --purge of base docker image packages before installing new ones. (sonic-net#819)

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>