Zero-initialize sockaddr_in and sockaddr_un structs that we're about
to fill in and pass to bind() or connect(), to ensure we don't leave
possible implementation-defined extension fields as uninitialized
garbage.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20210813150506.7768-3-peter.maydell@linaro.org