This is necessary to allow the user to disable peeking with
offset once it's enabled.
Unix sockets already allow the above, with this patch we
permit it for udp[6] sockets, too.

Fixes: 627d2d6b ("udp: enable MSG_PEEK at non-zero offset")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>