net/socket: fix Uninitialized scalar variable

If is_connected parameter is false, the saddr
variable will no initialize. Coverity report:
uninit_use: Using uninitialized value saddr.sin_port.

We don't need add saddr information to nc->info_str
when is_connected is false.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>