OPNSense/src 39c0abdsys/dev/netmap if_vtnet_netmap.h, sys/dev/virtio/network if_vtnet.c if_vtnetvar.h

MFC r340436

vtnet: fix netmap support

netmap(4) support for vtnet(4) was incomplete and had multiple bugs.
This commit fixes those bugs to bring netmap on vtnet in a functional state.

Changelist:
  - handle errors returned by virtqueue_enqueue() properly (they were
    previously ignored)
  - make sure netmap XOR rest of the kernel access each virtqueue.
  - compute the number of netmap slots for TX and RX separately, according to
    whether indirect descriptors are used or not for a given virtqueue.
  - make sure sglist are freed according to their type (mbufs or netmap
    buffers)
  - add support for mulitiqueue and netmap host (aka sw) rings.
  - intercept VQ interrupts directly instead of intercepting them in txq_eof
    and rxq_eof. This simplifies the code and makes it easier to make sure
    taskqueues are not running for a VQ while it is in netmap mode.
  - implement vntet_netmap_config() to cope with changes in the number of queues.

Reviewed by:    bryanv
Approved by:    gnn (mentor)
Sponsored by:   Sunny Valley Networks
Differential Revision:  https://reviews.freebsd.org/D17916
DeltaFile
+320-212sys/dev/netmap/if_vtnet_netmap.h
+36-34sys/dev/virtio/network/if_vtnet.c
+6-0sys/dev/virtio/network/if_vtnetvar.h
+362-2463 files

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