lib: rename parameter of bt_self_component_filter_add_{in,out}put_port

lib: rename parameter of bt_self_component_filter_add_{in,out}put_port

This makes is consistent with corresponding functions for sources and
sinks.  It will help for a future patch that will re-work the SWIG
bindings to have the same name everywhere (to apply the same typemap to
all of these).

Change-Id: Icdeb32711e56d4b6a619a493a8b64817f3084bd5
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1534
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>