refactoring of `named_config_getipandkeylist`

refactoring of `named_config_getipandkeylist`

Function `named_config_getipandkeylist()` processes the nested lists by
overriding the current local variable of the function, jumping back to
the beginning of the list processing. Of course, in order to go back to
the previous state and process the remaining items of the current list,
a "stack" array is used in order to put and get back the next list
element and associated values.

This makes the logic quite complex and error prone. Instead, this commit
changes the logic by recursing into the nested list (while sharing a
state between all the invocations). The processing is fundamentally
identical, but instead of "manually" handling the stack to go back to
the previous state (and process remaining elements of the current list),
takes advantage of recursion.