LAG upgrade - 15: updating standard member port statistics agent mapper routines

Updated #standard member port statistics agent mapper routines in LAG module. The agent #iterator routines and #mapper #routine has been updated to use standard member port entry based #indexing. This will access the port entries by using the #native #indexing. This removes references to the standard member port statistics indexing used earlier.

#LAG update 23 ...
[commit eeb9758ca6c1f4ddfdc56490d8c8f565d6cce56c] (https://github.com/nes-repo/NES-Open-Switch/commit/eeb9758ca6c1f4ddfdc56490d8c8f565d6cce56c)