telemetry: add client feature and sockets

telemetry: add client feature and sockets

This patch introduces clients to the telemetry API.

When a client makes a connection through the initial telemetry
socket, they can send a message through the socket to be
parsed. Register messages are expected through this socket, to
enable clients to register and have a client socket setup for
future communications.

A TAILQ is used to store all clients information. Using this, the
client sockets are polled for messages, which will later be parsed
and dealt with accordingly.

Functionality that make use of the client sockets were introduced
in this patch also, such as writing to client sockets, and sending
error responses.

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>