Updating sonic-swss-common submodule

> Add a new field for FLEX_COUNTER_TABLE to indicate delay for flex counters (sonic-net#523)
> [logger] Make map access thread safe and proper terminate thread (sonic-net#510)
> Test with coverage output, publish gcov on Azure pipelines (sonic-net#517)
> Update schema.h to include config_db DHCP and state_db counter table (sonic-net#521)
> [schema] Add next hop group table to schema (sonic-net#475)
> Fix: DBInterface::get() return nullable strings (sonic-net#516)
> [netlink]refill netlink cache when failing to get the link object by name. (sonic-net#506)
> Fix test_ConfigDBSubscribe timing risk (sonic-net#512)
> added missing headers for building with gcc-10.3 (sonic-net#494)
> Modify the hardcode separator ":" to variable. (sonic-net#473)

Author: TACappleman