IP TOS bits mask value. It identifies the portion of
agentDiffServAuxMfClfrTos that is compared against a packet.
A non-contiguous mask value is permitted. A mask of 0 indicates a match
of any TOS value.
There are multiple, overlapping meanings of the TOS octet in use today.
These are represented by the following specific mask values:
Precedence (bits 7-5): 224 (bit mask '11100000')
DSCP (bits 7-2): 252 (bit mask '11111100')
TOS (bits 7-0): 255 (bit mask '11111111')
Other mask values are also permitted.