Improve debuggablity

[yue-fred-gao]

Debuggability at SONIC-VPP SAI layer is poor. If we turn on syncd debug log, it becomes too chatty because that's the level logged by SWSS_LOG_ENTER. And the latter doesn't print arguments. Also, major operations are not logged either.

Proposals

1. Use SWSS_LOG_INFO. It is not turned on by default and it is above debug level so won't be overwhelmed by debug messages.
2. All VPP API calls should be logged as INFO with parameters.
3. Create/set/remove requests from syncd should be logged as INFO with arguments
4. Other important logs can be added as needed.