[sonic-swss-common][sonic-snmpagent] Update submodule (#8357)

Include below commits

sonic-swss-common
```
83d3351 2021-04-22 | [swig] fix ConfigDBConnector.db_name (sonic-net#483) [Qi Luo]
fdf296f 2021-04-09 | Fix: ConfigDBConnector call super init with proper parameter name (sonic-net#470) [Qi Luo]
4f580e3 2021-03-26 | [swig] translate SonicV2Connector::keys return type from C++ vector<string> to Python list (sonic-net#468) [Qi Luo]
```

sonic-snmpagent
```
c160c2b 2021-08-04 | CPU Spike because of redundant and flooded keyspace notifis handled (sonic-net#230) [Vivek Reddy]
a4dd3bf 2021-08-03 | Non-block reading counters to tolerate corrupted/delayed counters in COUNTERS_DB (sonic-net#231) [Qi Luo]
```