Bluetooth: Create generic queue_monitor_skb helper function

The hci_send_to_monitor function contains generic code for queueing the
packet into the receive queue of every monitor client. To avoid code
duplication, create a generic queue_monitor_skb function to interate
over all monitor sockets.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>