PACKET_RX_RING allows the use of an mmapped buffer to receive packets from the
kernel. This should cut down the number of host syscalls that need to be made
to receive packets when the underlying fd is a socket of the AF_PACKET type.
PiperOrigin-RevId: 233834998
Change-Id: I8060025c6ced206986e94cc46b8f382b81bfa47f
Bhasker Hariharan