LAG upgrade - 11: updating member port list agent mapper routines

Updated #member #port #list agent routines in LAG module. The agent #iterator routines and #mapper #routine has been updated to use #aggregator #based #indexing. This will access the member list embedded in the aggregator and there by removing the redundant indexing.

#LAG update 19 ...
[commit ae96877c7d1a4d0e4a3ba3eef97b522bd0fcbafd] (https://github.com/nes-repo/NES-Open-Switch/commit/ae96877c7d1a4d0e4a3ba3eef97b522bd0fcbafd)