drbd: Fix resource role for newly created resources in events2

The conn_higest_role() (a terribly misnamed function) returns
the role of the resource. It returned R_UNKNOWN as long as the
resource has not a single device.

Resources without devices are short living objects.

But it matters for the NOTIFY_CREATE netwlink message. It makes
a lot more sense to report R_SECONDARY for the newly created
resource than R_UNKNOWN.

I reviewd all call sites of conn_highest_role(), that change
does not matter for the other call sites.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>