[snmpagent] update submodule (sonic-net#6169)

Includes below sonic-snmpagent commits
```
dfde06e 2021-01-13 | Revert "[rfc1213] Interface MIB add l3 vlan interfaces & aggregate rif counters (#169)" (#191) [Stepan Blyshchak]
45edd7e 2021-01-04 | [snmpagent] Fix hardcoded qsfp lane count by reading sensor status from DB (#184) [Junchao-Mellanox]
3b72a6f 2021-01-02 | Fix: handle empty LOC_CHASSIS_TABLE (#190) [Qi Luo]
4aad821 2020-12-29 | [sysName]: Implement sysName OID (#185) [SuvarnaMeenakshi]
8efb4bb 2020-12-29 | [rfc1213] fix counter value type (#189) [Stepan Blyshchak]
025483a 2020-12-23 | [RouteUpdater]: Fix multi_asic mock function implementation and multi_asic variable name (#186) [SuvarnaMeenakshi]
381ae47 2020-12-10 | [mibs] b'VLAN_TABLE:' -> 'VLAN_TABLE' (#181) [Stepan Blyshchak]
e54036c 2020-12-09 | [rfc1213] Interface MIB add l3 vlan interfaces & aggregate rif counters (#169) [Stepan Blyshchak]
fd1eae7 2020-11-24 | Set swsscommon logging level (#178) [Qi Luo]
706d504 2020-11-23 | Improve MockRedis _encode(): so it will work on all types of value (#179) [Qi Luo]
64c93a1 2020-11-16 | [RFC4292][Namespace]: Fix implementation of RouteUpdater for multi-asic platform (#176) [SuvarnaMeenakshi]
b8f19ee 2020-11-12 | [sonic-snmpagent] SONiC physical entity mib extension (#168) [Junchao-Mellanox]
6b94ec3 2020-11-05 | Replace swsssdk.SonicV2Connector with swsscommon.SonicV2Connector (SWIG wrapper of C++ implementation) in production code (#162) [Qi Luo]
```

Signed-off-by: Stepan Blyshchak <stepanb@nvidia.com>
Co-authored-by: Qi Luo <qiluo-msft@users.noreply.github.com>