libbpf: Change hash_combine parameters from long to unsigned long

libbpf: Change hash_combine parameters from long to unsigned long

The hash_combine() could be trapped when compiled with sanitizer like "zig cc"
or clang with signed-integer-overflow option. This patch parameters and return
type to unsigned long to remove the potential overflow.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20241116081054.65195-1-sidong.yang@furiosa.ai
Signed-off-by: Alexei Starovoitov <ast@kernel.org>