libbpf: fix to reject unknown flags in xsk_socket__create()
In xsk_socket__create(), the libbpf_flags field was not checked for
setting currently unused/unknown flags. This patch fixes that by
returning -EINVAL if the user has set any flag that is not in use at
this point in time.
Fixes: 509c34c8565b ("libbpf: add support for using AF_XDP sockets") Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com> Reviewed-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>