fault injection: disable stacktrace filter for x86-64

Disable stacktrace filter support for x86-64 for now.  Will be enable when we
can get the dwarf2 unwinder back.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>