Merge branch 'vhost_net-batching'

Jason Wang says:

====================
vhost_net tx batching

This series tries to implement tx batching support for vhost. This was
done by using MSG_MORE as a hint for under layer socket. The backend
(e.g tap) can then batch the packets temporarily in a list and
submit it all once the number of bacthed exceeds a limitation.

Tests shows obvious improvement on guest pktgen over over
mlx4(noqueue) on host:

                                     Mpps  -+%
        rx-frames = 0                0.91  +0%
        rx-frames = 4                1.00  +9.8%
        rx-frames = 8                1.00  +9.8%
        rx-frames = 16               1.01  +10.9%
        rx-frames = 32               1.07  +17.5%
        rx-frames = 48               1.07  +17.5%
        rx-frames = 64               1.08  +18.6%
        rx-frames = 64 (no MSG_MORE) 0.91  +0%

Changes from V4:
- stick to NAPI_POLL_WEIGHT for rx-frames is user specify a value
  greater than it.
Changes from V3:
- use ethtool instead of module parameter to control the maximum
  number of batched packets
- avoid overhead when MSG_MORE were not set and no packet queued
Changes from V2:
- remove uselss queue limitation check (and we don't drop any packet now)
Changes from V1:
- drop NAPI handler since we don't use NAPI now
- fix the issues that may exceeds max pending of zerocopy
- more improvement on available buffer detection
- move the limitation of batched pacekts from vhost to tuntap
====================

Signed-off-by: David S. Miller <davem@davemloft.net>