bluetooth_sendto() uses netdev_findbyindex(conn->bc_ldev + 1) to find
the Bluetooth network device for an HCI socket. netdev_findbyindex
searches by global interface index, but bc_ldev is a 0-based count of
Bluetooth devices only — it bears no fixed relationship to the global
interface index. If any netdev other than a Bluetooth device is
registered before it (e.g. loopback or Ethernet), the Bluetooth device
will not be at global index bc_ldev + 1 and the lookup will return NULL
or the wrong device.
Fix this by replacing netdev_findbyindex with a netdev_foreach walk
using a small callback (bluetooth_dev_byidx_callback) that counts only
NET_LL_BLUETOOTH devices and returns the bc_ldev-th one, regardless of
what else is registered or in what order.
Signed-off-by: Stephen Fox <stephenfox@geotab.com>
990ac856b2