Bluetooth: Host: Avoid memcpy'ing bt_addr_t to same pointer

From le_ext_adv_param_set we will occasionally attempt
to call bt_addr_copy where the `addr` and &adv->random_addr.a
are the same pointer. Doing a memcpy where source and destination
is the same pointer is undefined behavior and should not be
done.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>