Add a microbenchmark for bpf_csum_diff() helper. This benchmark works by
filling a 4KB buffer with random data and calculating the internet
checksum on different parts of this buffer using bpf_csum_diff().
Example run using ./benchs/run_bench_csum_diff.sh on x86_64:
[bpf]$ ./benchs/run_bench_csum_diff.sh
4 2.296 ± 0.066M/s (drops 0.000 ± 0.000M/s)
8 2.320 ± 0.003M/s (drops 0.000 ± 0.000M/s)
16 2.315 ± 0.001M/s (drops 0.000 ± 0.000M/s)
20 2.318 ± 0.001M/s (drops 0.000 ± 0.000M/s)
32 2.308 ± 0.003M/s (drops 0.000 ± 0.000M/s)
40 2.300 ± 0.029M/s (drops 0.000 ± 0.000M/s)
64 2.286 ± 0.001M/s (drops 0.000 ± 0.000M/s)
128 2.250 ± 0.001M/s (drops 0.000 ± 0.000M/s)
256 2.173 ± 0.001M/s (drops 0.000 ± 0.000M/s)
512 2.023 ± 0.055M/s (drops 0.000 ± 0.000M/s)
Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx>