Bluetooth: L2CAP: Don't return -EAGAIN if out of credits

Just keep queueing them into TX queue since the caller might just have
to do the same and there is no impact in adding another packet to the
TX queue even if there aren't any credits to transmit them.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>