The three options handling `struct sock_fprog` (TUNATTACHFILTER,
TUNDETACHFILTER, and TUNGETFILTER) are not implemented. Linux kernel
keeps a user space pointer in them which we cannot correctly handle.

Signed-off-by: Josh Kunz <jkz@google.com>
Signed-off-by: Shu-Chun Weng <scw@google.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200929014801.655524-1-scw@google.com>
[lv: use 0 size in unlock_user()]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>