Hexstring RAW fix (#issue 557)

The RAW encoding of hextring with
- FIELDORDER(msb)
- HEXORDER(high)
- Field starts on half octet
fails

The hexstring starting of half octet is handled specially as only the hex digits in the whole octets should be swapped.
Because the buffer is filled diferently in the case of different FIELDORDER, the hex digit swapping should be adopted to the FIELDORDER

Signed-off-by: Gabor Szalai <gabor.szalai@ericsson.com>