selftests/bpf: Fix "dubious pointer arithmetic" test

The verifier trace changed following a bugfix. After checking the 64-bit
sign, only the upper bit mask is known, not bit 31. Update the test
accordingly.

Signed-off-by: Jean-Philippe Brucker <[email protected]>
Acked-by: John Fastabend <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
1 file changed