The specific packet string representing the
destination address, source address, type/length
field and a window of 64 bytes of packet data
beginning at DataOffset to be used for filtering
decisions. Each ASCII character of the string
represents a nibble of packet data, therefore the
packet string should be (14+64) * 2 = 156 characters
long. A value of 'x' in the packet string is
used to indicate a 'Don't care' and no filtering is
to be performed on that nibble. The string may be
be of size 0 to 78 bytes. If a size less than 78
bytes is used, the string will still begin at the
destination address.