Fix: implicit conversion of enum types in consumer

This actually remove the use of LTTNG_ERR* code in the sessiond/consumer
protocol since it should NOT be used and some comparison of enum
(lttng_error_code vs lttcomm_return_code) were broken and dangerous.

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: implicit conversion of enum types in sessiond

Signed-off-by: David Goulet <dgoulet@efficios.com>