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.h

@@ -42,5 +42,6 @@ void free_byte_array(byte_array_t ba);
 bool eq_byte_array(const byte_array_t* m0, const byte_array_t* m1);
 
 byte_array_t cp_str_to_ba(const char* str);
+char* cp_ba_to_str(const byte_array_t ba);
 
 #endif