Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Fix an error in our results printing.

Change the output of mctest to give a summary of the results instead
of printing a long list.

Add a default base port, and default mulitcast address to the
runner script.

Add support for specifying a different local and remote interface
in the runner script.

MFC after: 1 week

Fixed error checking of pthread(3) functions.

PR: 143807
Submitted by: pluknet (partly)

Update mctest and its associated script to have a base port to listen
on so that multiple copies can be run easily.

Update documentation with group and port arguments which are optional.

Updated the test to handle multiple sinks. The sinks cut their
transmissions by the number of them running so that they do not
overwhelm the source.

Added a simple shell script to kick off sinks on multiple hosts as
well as a source on the host where the shell script is run. The script
also collects the output of all the sinks and the source into files named
for the host on which the tests are run. A date is appended to each output
file to make it unique per run.

Add a manual page and a Makefile.

Add code to reflect packets back from the sink so that we can measure
round trip at the source.

Add the correct license.

A multicast test. The mctest program acts as both a source and a sink
for multicast packets. Parameters for the interface, packet size,
number of packets, and interpacket gap may be given on the command line.
The sink records how many packets were missed, and at what time each
packet arrived.