Correctly link function

ran_func_kpm.c uses cp_ba_to_str(), but it is not defined in OAI. Define
it so we can link properly, instead of relying on FlexRIC (where it was
defined).

common/utils/ds/byte_array.c

@@ -72,3 +72,17 @@ byte_array_t cp_str_to_ba(const char* str)
 
   return dst;
 }
+
+char* cp_ba_to_str(const byte_array_t ba)
+{
+  assert(ba.len > 0);
+
+  const size_t sz = ba.len;
+  char* str = calloc(sz+1, sizeof(char));
+  assert(str != NULL && "Memory exhausted");
+
+  memcpy(str, ba.buf, sz);
+  str[sz] = '\0';
+
+  return str;
+}