Bluetooth: Add flags field and setting function for HCI sockets

To filter out certain actions for certain HCI sockets introcuce a flags
field that allows to configure specific settings on individual sockets.

Since the hci_pinfo structure is private in hci_sock.c, provide helper
functions for setting and clearing a given flag.

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