[Submodule Update] sonic-utilities Following Changes:

[fwutil]: Use overlay driver when mounting next image filesystem (sonic-net#825)
Fix for adding L3 interface to Vlan group (sonic-net#826)Fix for adding L3 interface to Vlan group (sonic-net#826)
[db_migrator]Do DB migration for buffer pool size change on Mellanox platform (sonic-net#833)
explicitly specify command with underscores (sonic-net#846)
[intfutil] set speed to 0 when interface speed is not available (sonic-net#839)