LAG upgrade - 21: updating custom aggregator agent mapper routines

Updated #custom aggregator agent routines in LAG module. The agent #iterator routines and #mapper #routine has been updated to use standard #aggregator #based #indexing. This will access the custom aggregator entries #embedded in the standard #aggregator entries and there by removing the redundant indexing. The custom aggregator entries contain attributes like the #aggregator-group, #max-bandwidth, etc ...

#LAG update 29 ...
[commit 09b87ee92cf898c0f940626591f89ff4dc27faec] (https://github.com/nes-repo/NES-Open-Switch/commit/09b87ee92cf898c0f940626591f89ff4dc27faec)