net: Add UDP multicast support

Allow UDP readers to listen to UDP multicast traffic if hostname is set
to a valid UDP multicast address.

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
net: Allow setting network interface to use for multicast

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
net: Add option to set outgoing multicast TTL

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
net: Add UDP multicast example job file

This adds a pingpong UDP multicast example with two readers.

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>