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