samples/seccomp: fix 64-bit comparison macros

There were some bugs in the JNE64 and JLT64 comparision macros. This fixes
them, improves comments, and cleans up the file while we are at it.

Reported-by: Stephen Röttger <sroettger@google.com>
Signed-off-by: Mathias Svensson <idolf@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>