af_packet.WritePacketData via packet mmap

It would be very convenient if af_packet was able to send packets to a network card via the packet_mmap interface.

Why to send packets also need high performance:

1. For writing benchmarks for programs that use gopacket to decode packets (for example, I now have the task to check the performance of package decoding + data parsing from the application layer).
2. Applications that monitor the network should be able to respond quickly to dangerous traffic.