[PATCH v2 1/4] ws2_32/tests: Use %u and %zu in test_ipv6_cmsg instead of casting

[Zebediah Figura (she/her)]

Sorry, I suggested %zu, but I get warnings here when actually using it 
with mingw. IIRC only ucrtbase (and recent versions of msvcrt?) actually 
support it anyway, so I guess %Iu is the right solution.