lib: increase maximal MIP version number

lib: increase maximal MIP version number

We are going to introduce MIP version 1, so adjust
bt_get_maximal_mip_version accordingly.

Change-Id: I6d698d252dbcd60c81b9355bc378e0a4fc7f425e
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7313
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7197