in .config/net.supertuxkart/supertuxkart/config-0.10/config.xml, around line 465, is the setting still at 0?
463
464 <!-- Status of internet: 0 user wasn't asked, 1: allowed, 2: not allowed -->
465 <enable_internet value="1" />
466
Try toggling it to 1 or 2 and see what happens 