bpf: Check tail zero of bpf_common_attr using offsetofend

bpf: Check tail zero of bpf_common_attr using offsetofend

Because of the 8-byte alignment, the compiler will pad struct
bpf_common_attr to 24 bytes. That said, sizeof(attr_common) is 24 instead
of 20.

When check tail zero using sizeof(attr_common) in
bpf_check_uarg_tail_zero(), there will be 4 bytes that won't be checked.

To also check the padding 4 bytes, replace sizeof(attr_common) with
offsetofend(struct bpf_common_attr, log_true_size).

Fixes: f28771c0691b ("bpf: Extend BPF syscall with common attributes support")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260518145446.6794-2-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>