Fix pointer alignment bug causing SIGBUS on Sparc64

OK, the issue was related to the alignment issue between the
thread_options structure and its "packed" version : The lexxx_to_cpu
macros are incorrectly casting the pointers and that causes an bus
error.  I have fixed the issue by avoid casting the pointers and calling
directly the "swap" method.

I have also included a fixed on the thread_options structure regarding
the ddir_seq_add variable : Its length was incorrect.

Signed-off-by: Jens Axboe <axboe@fb.com>