Changes

asp: Introduce asp->assoc_as_list

This way we can iterate easily/quickly the AS served by a given ASP.
This in turn allows simplifying some code since we cache the amount of
AS served by the ASP at any time, so we save some counting.

Related: SYS#6953
Change-Id: I1ca90748286374109dbb4277cbc7b2337ce2072a