ngap_pdu_t has the same definition as byte_array_t, so it is
replaced by the latter. This simplify the stack and reduces
duplicated code.
Also, add function create_byte_array to copy from an
existing buffer to a new byte_array_t and replaced
allocCopy with create_byte_array, and adopted
OCTET_STRING_fromBuf whenever possible.
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).
Using AssertFatal() has the drawback that it requires the definition of
an exit_function() (which is typically declared in OAI main
executables). We don't want to pull in such dependency for every
consumer. Hence, use c stdlib's assert() instead.