Bluetooth: hci_sock: Reset cookie to zero in hci_sock_free_cookie()

Reset cookie value to 0 instead of 0xffffffff in hci_sock_free_cookie()
since:
0 : means cookie has not been assigned yet
0xffffffff: means cookie assignment failure

Also fix generating cookie failure with usage shown below:
hci_sock_gen_cookie(sk) // generate cookie
hci_sock_free_cookie(sk) // free cookie
hci_sock_gen_cookie(sk) // Can't generate cookie any more

Signed-off-by: Zijun Hu <[e-mail]>
Signed-off-by: Luiz Augusto von Dentz <[e-mail]>

net/bluetooth/hci_sock.c

···
 	int id = hci_pi(sk)->cookie;
 
 	if (id) {
-		hci_pi(sk)->cookie = 0xffffffff;
+		hci_pi(sk)->cookie = 0;
 		ida_free(&sock_cookie_ida, id);
 	}
 }