'extern "C"' not needed here

1) 'extern "C"' not needed here
2) We need to adhere to AMUSE standards, I guess the legacy decorator implies that we need to set an argument 'int * value' and '*value = jd->get_nj_max(); return 0;' or we will be returned an empty list instead of an integer.
3) As a consequence of 2) we need to add an argument to the function: 'function.addParameter(...'.

Author: HannoSpreeuw

src/amuse_ph4/interface.py

@@ -464,8 +464,11 @@ def recompute_timesteps():
         function.result_type = 'int32'
         return function
 
+    @legacy_function
     def get_nj_max():
         function = LegacyFunctionSpecification()
+        function.addParameter('nj_max', dtype='int32',
+                              direction=function.OUT)
         function.result_type = 'int32'
         return function