High Performance UML Vector Network Driver

1. Provides infrastructure for vector IO using recvmmsg/sendmmsg.
    1.1. Multi-message read.
    1.2. Multi-message write.
    1.3. Optimized queue support for multi-packet enqueue/dequeue.
    1.4. BQL/DQL support.
2. Implements transports for several transports as well support
for direct wiring of PWEs to NIC. Allows direct connection of VMs
to host, other VMs and network devices with no switch in use.
    2.1. Raw socket >4 times higher PPS and 10 times higher tcp RX
    than existing pcap based transport (> 4Gbit)
    2.2. New tap transport using socket RX and tap xmit. Similar
    performance improvements (>4Gbit)
    2.3. GRE transport - direct wiring to GRE PWE
    2.4. L2TPv3 transport - direct wiring to L2TPv3 PWE
3. Tuning, performance and offload related setting support via ethtool.
4. Initial BPF support - used in tap/raw to avoid software looping
5. Scatter Gather support.
6. VNET and checksum offload support for raw socket transport.
7. TSO/GSO support where applicable or available
8. Migrates all error messages to netdevice_*() and rate limits
them where needed.

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>