Access union value_data members consistently

Access union value_data members consistently

Use the same, appropriate union value_data member for each access of
BOOLEAN, BYTE and SHORT PW_TYPEs, without assuming they're
interchangeable with "integer", as that is only true on little-endian
architectures.

This fixes at least this wimax unit test failure on s390x and ppc64:

    Mismatch in line 11 of src/tests/unit/wimax.txt, got: 1a 0c 00 00 60 b5 01 06 00 02 03 00 expected: 1a 0c 00 00 60 b5 01 06 00 02 03 01