This option enables packet level marking of HIT/MISS responses,
	either using IP TOS or socket priority.
	    off		Feature disabled
	    tos		Set the IP TOS/Diffserv field
	    priority	Set the socket priority (may get mapped to TOS by OS,
			otherwise only usable in local rulesets)
	    option	Embed the mark in an IP option field. See also
	    		zph_option.

	See also tcp_outgoing_tos for details/requirements about TOS usage.