LAG upgrade - 19: updating standard extended member port agent mapper routines

Updated #standard #extended #member #port agent routines in LAG module. The agent #iterator routines and #mapper #routine has been updated to use standard #member #port #based #indexing. This will access the extended member port entries #embedded in the standard #member #port entries and there by removing the redundant indexing. The standard extended member port entries contain #attributes like the #custom #destination #address for the #LACP control and marker #PDUs.

#LAG update 27 ...
[commit bc7c27612e082a5ff1fea525aee47d42a1a54611] (https://github.com/nes-repo/NES-Open-Switch/commit/bc7c27612e082a5ff1fea525aee47d42a1a54611)