The 'on' variable is never used, and 'off' is only used
if IPV6_V6ONLY is defined; delete 'on' and move 'off' to
the point where it is used. This avoids warnings from
clang 3.4.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>