Fix order dependency between cache_dir and maximum_object_size

Fix order dependency between cache_dir and maximum_object_size

parse_cachedir() has a call to update_maxobjsize() which limits the
store_maxobjsize variable used as the internal maximum_object_size
variable of the store data structure) to the value of maximum_object_size
defined at the moment of execution of this function, for all stores (all
store directories). So if parse for cache_dir is called before
maximum_object_size, we get the effect of the default 4 MB.

BUT, when we get to parse maximum_object_size line(s) after the last
cache_dir, the maximum_object_size option is processed and only shown on
the cachemgr config page without having updated store_maxobjsize.