Fix: Don't create a new packet if ctf_move_pos() seeks out of a packet

This change ensures that ctf_move_pos() does not create a new packet
when ctf_move_pos() moves out of the current packet's bounds. The next
call to ctf_pos_access_ok() will report EFAULT which can then be
handled appropriately by the caller.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add public CTF Writer API headers

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add CTF Writer implementation

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tests: Add a CTF Writer test

The test will be ran as part of the "tests" test plan.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>