Rename LTTng index in CTF index

Also the magic becomes a uint32_t instead of 6 chars for more aligned
reads.

Apart from the CTF magic changes, this patch only renames stuff so no
behaviour is changed.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: don't fail on push metadata if no channel

The comments in the code explains it well but in a nutshell, this is an
acceptable race between the creation of the metadata on the consumer
side and the push metadata from the session daemon for that channel.

This race is resolved by either having the consumer requesting metadata
or the session is stopped which will in both situation push the metadata
to the consumer.

Without that fix, the session daemon flags the registry's metadata to be
"closed" which usually indicates that the consumer is not responding
leading to the consumer thread exiting in the session daemon.

Acked-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: update back the metadata len sent on failure

Acked-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: missing lock/unlock when sending index

This was creating out of order messages between the relayd and the
consumer leading to undesired behaviour for the tracing session being
streamed.

Acked-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: remove assert on fd in the read/write layer

It is possible that an invalid fd is passed to read or write. This can
happen for instance if the endpoint of the transport (ex: relayd) dies
out while actively trying to send data. It is OK to let an invalid fd
where the syscall will return the right value along with errno being
populated with the corresponding code.

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