fanotify: use __aligned_u64 in fanotify userspace metadata

Currently the userspace struct exposed by fanotify uses
__attribute__((packed)) to make sure that alignment works on multiarch
platforms.  Since this causes a severe performance penalty on some
platforms we are going to switch to using explicit alignment notation on
the 64bit values so we don't have to use 'packed'

Signed-off-by: Eric Paris <eparis@redhat.com>