Bluetooth: hidp: merge 'send' functions into hidp_send_message()

We handle skb buffers all over the place, even though we have
hidp_send_*_message() helpers. This creates a more generic
hidp_send_message() helper and uses it instead of dealing with transmit
queues directly everywhere.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>