Extensions to the netmap framework - Week 9

[Stefano Duo]

Hi,

during this past week i added support for per-ring fixed offsets.
The library net/netmap_user.h has been changed accordingly and applications
will automatically handle the offsets through the NETMAP_BUF() macro after
being re-compiled.

This type of offset can be specified during a NETMAP_REQ_REGISTER command
by adding a struct nmreq_opt_ring_offset to the option list. The offset
will be applied to each ring specified by the register request with the
exception of netmap pipes and monitors:
- netmap pipes apply the offset to every ring of both ends, regardless of
the specified rings.
- netmap monitors retrieve the offset from the monitored rings, therefore
it is considered an error if an application specifies an offset during the
register command, or if the specified rings to monitor have been registered
with different offsets.

Project wiki:
https://wiki.freebsd.org/SummerOfCode2018Projects/ExtensionsToNetmap
SVN repository: https://svnweb.freebsd.org/socsvn/soc2018/sduo/

Stefano.