make Network Component FS interface functions weak again

[andbararm]

Before Middleware 8, the FS interface functions for the different network services, like FTP server, had the weak attribute. This enabled users to also reimplement these functions to use different File Systems.
In Middleware 8, the weak attribute is not present any more, which prevents the possibility to reimplement those functions.
To bring back this option, the weak attribute should be added again.