Avoid assert on non-implemented SM write callback

The asserts might be used to intentionally stop the running process.
Further, it might be an annoyance if it happen unintentionally. Just
print an error message instead, and return to FlexRIC that nothing is to
be sent.

openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_kpm.c

@@ -537,7 +537,7 @@ void read_kpm_setup_sm(void* e2ap)
 
 sm_ag_if_ans_t write_ctrl_kpm_sm(void const* src)
 {
-  assert(0 !=0 && "Not supported");
+  printf("write_ctrl callback for KPM SM: operation not supported\n");
   (void)src;
   sm_ag_if_ans_t ans = {0};
   return ans;