Bluetooth: mgmt_stop_discovery_failed()

This patches creates mgmt_stop_discovery_failed() which removes
pending MGMT_OP_STOP_DISCOVERY commands and sends proper command
status events.

This patch also fixes the MGMT_OP_STOP_DISCOVERY command leak in
case cancel inquiry fails.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>