Use consumer fd reference in consumer socket obj

This is done so we don't copy the fd value of the consumer thus having a
central control. This is part of a set of patches that makes the session
daemon stop sending command to an invalid consumer (dead, closed).

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>