LAG upgrade - 28: added LAG interface OPER-STATUS handler

Added #aggregator logical-interface ( #lag-interface ) #OPER-STATUS #handler routine in LAG module. This enables to #perform the #support #procedures for #lag-interfaces on OPER-STATUS change. The handler is registered with the IF module and #IF #module will #execute this #call-back on respective #parameter #change in IF module. This helps to perform the necessary procedures in LAG module when the OPER-STATUS is changed from IF module. The references to the augmented custom aggregator data-structures has been updated to the standard aggregator data-structures.

#LAG update 36 ...
[commit 53be9578d6d937bfe18fad3d7c1efffc69722550] (https://github.com/nes-repo/NES-Open-Switch/commit/53be9578d6d937bfe18fad3d7c1efffc69722550)