Bluetooth: Simplify packet copy in hci_send_to_monitor function

Within the monitor functionality, the global atomic variable called
monitor_promisc ensures that no memory allocation happend when there
is actually no client listening. This means it is safe to just create
a copy of the skb since it is guaranteed that at least one client
exists. No extra checks needed.

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