[submodule]: retreat sonic-swss submodule

retreat two commits which cause warm reboot regression

* eb79ca4 2021-09-01 | [pbh]: Add PBH OA (sonic-net#1782) [Nazarii Hnydyn]
* 3d6b1f0 2021-08-31 | [buffer orch] Bugfix: Don't query counter SAI_BUFFER_POOL_STAT_XOFF_ROOM_WATERMARK_BYTES on a pool where it is not supported (sonic-net#1857) [Stephen Sun]

Signed-off-by: Guohan Lu <[email protected]>