MFC r339717, r339749, and r339809.

r339717:
cxgbe(4): Allow "pass" filters to distribute matching traffic using a
subset of a VI's RSS indirection table.

This makes it possible to make groups out of rx queues and steer
different kinds of traffic to different groups. For example, an
interface with 8 rx queues could have all non-TCP traffic delivered to
queues 0-3 and all TCP traffic to queues 4-7.

Note that it is already possible for filters to steer traffic to a
particular queue or to distribute it using the full indirection table
(much like normal rx does).

Sponsored by: Chelsio Communications

r339749:
cxgbe(4): Add a knob to split the rx queues for a netmap enabled
interface into two groups. Filters can be used to match traffic
and distribute it across a group.

hw.cxgbe.nm_split_rss

Sponsored by: Chelsio Communications

r339809:
cxgbetool(8): Add a subaction (tcbrss <n>) that can be used with "pass"
action to distribute traffic using the half of the VI's RSS indirection
table.

The value specified should either be the start of the VI's RSS slice
(available at dev.<ifname>.<inst>.rss_base since r339700) or the
midpoint (rss_base + rss_size/2). The traffic that hits the filter will
use the first or second half of the indirection table respectively.
The indirection table can be populated in different ways to achieve
different kinds of traffic/load distributions. For example, r339749
allows a netmap interface to have half the rx queues in the first half
of the table and the rest in the other.

Sponsored by: Chelsio Communications