Initial import of the new binary lttng-relayd

Initial import of the new binary lttng-relayd

The lttng-relayd listens on the network and receives traces streamed by
the consumer.

At this first commit, the relayd supports IPv4 and IPv6 over TCP.

The following commits will add the support to use it with the lttng
command line interface, control library, consumer and session daemon.

Signed-off-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>