telemetry: add initial connection socket

telemetry: add initial connection socket

This patch adds the telemetry UNIX socket. It is used to
allow connections from external clients.

On the initial connection from a client, ethdev stats are
registered in the metrics library, to allow for their retrieval
at a later stage.

Signed-off-by: Ciara Power <ciara.power@intel.com>
Signed-off-by: Brian Archbold <brian.archbold@intel.com>
Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>