Packet Mark is an analogue to ipfw tags with O(1) lookup from mbuf while
regular tags require a single-linked list traversal.
Mark is a 32-bit number that can be looked up in a table
[with 'number' table-type], matched or compared with a number with optional
mask applied before comparison.
Having generic nature, Mark can be used in a variety of needs.
For example, it could be used as a security group: mark will hold a security
group id and represent a group of packet flows that shares same access
control policy.
Reviewed By: pauamma_gundo.com
Differential Revision: https://reviews.freebsd.org/D39555
MFC after: 1 month
fc727ad63d