Fix: reset out_fd_offset when we rotate the trace file

This value is only used for the sync_file_range, but it has to be set
to 0 when we start to write in a new trace file, otherwise the values
passed to this call are bogus.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Generate local kernel and UST indexes

When the consumer creates a new trace file, it now creates as well an
index file that the viewers can use to navigate in the trace.
For now these indexes are only local and not sent to the relayd.

This patch requires additionnal ioctl and ustctl calls implemented
in lttng-modules and lttng-ust in 2.4.

For now, if a tracefile size is specified, we don't generate any index.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
fix : support tracefile rotation

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>