Fix bug in fetching all values of a RADIUS AVP.

Using AVPs from script, you can now retrieve all the values (not only yhe first value of the RADIUS AVP).
In order to maintain backward compatibility, the fetch_all_values module parameter was added - by default is off.

Reported and tested by John Quick.

(cherry picked from commit 0ba0bf059d67fa28e1b9b4f40d4af86db77f5593)