Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Set default socket size for netreceive to 128k to reduce the chances
of the buffer overflowing before netreceive can be scheduled to read
the packets from the socket.

Add netrate (netreceive, netsend), a tool for generating (and sinking)
UDP packets of specified size at a fixed rate. I've been using this for
netperf-related testing.