Fix: python binding: expose domain buffer type

On enable_channel the domain buffer type is used to create a temporary
channel. This currently fail for kernel channel since the buffer type is
not exposed at the binding level and default to LTTNG_BUFFER_PER_PID.
Channel for the kernel domain can only be created in LTTNG_BUFFER_GLOBAL
mode.

Exposing the buffer type also allow userpsace channel to use the per uid
buffering scheme.

The current bindings are in a rough state. This is to at least get them
to work with kernel domain.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>