ksnoop: remove duplicate include

ksnoop: remove duplicate include

`ksnoop` is the only libbpf tool which is including both `<linux/bpf.h>` and `<bpf/bpf.h>` - the rest of the tools just include the latter

build fails for me because of redefinition errors as a result. Let's use `<bpf/bpf.h>` like the rest of the tools