Bluetooth: Require CAP_NET_ADMIN for HCI User Channel operation

The HCI User Channel operation is an admin operation that puts the
device into promiscuous mode for single use. It is more suitable
to require CAP_NET_ADMIN than CAP_NET_RAW.

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