bpf: Fix the xdp_adjust_tail sample prog issue

During the xdp_adjust_tail test, probabilistic failure occurs and SKB package
is discarded by the kernel. After checking the issues by tracking SKB package,
it is identified that they were caused by checksum errors. Refer to checksum
of the arch/arm64/include/asm/checksum.h for fixing.

v2: Based on Alexei Starovoitov's suggestions, it is necessary to keep the code
 implementation consistent.

Fixes: c6ffd1ff (bpf: add bpf_xdp_adjust_tail sample prog)
Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240930024115.52841-1-chenyuan_fl@163.com