RC: forward declarations and link physims better

The simulators have been changed: due to linker errors that would arise
otherwise, a lot of functions are defined in them to avoid such errors.
Some functions are also defined in header files; in this commit, we
define most functoins in nr_dummy_functions.c, which is compiled in, not
by including the C file, but by adding it to the target in
CMakeLists.txt

- nr_dlsim+nr_ulsim need NR_IF_Module_init(), so it cannot be in
  nr_dummy_functions, but the others need it
- Link correcr NR_IF_Module_init() into these simulators, and reduce
  overall link list
- Correctly link remaining simulators

openair2/LAYER2/MAC/pre_processor.c

@@ -806,6 +806,7 @@ void rr_ul_unset(void **data) {
     free(*data);
   *data = NULL;
 }
+#define MAX(a, b) (((a)>(b))?(a):(b))
 int rr_ul_run(module_id_t Mod_id,
               int CC_id,
               int frame,