xfs: make i_flags an unsigned long

To be used for bit wakeup i_flags needs to be an unsigned long or we'll
run into trouble on big endian systems.  Because of the 1-byte i_update
field right after it this actually causes a fairly large size increase
on its own (4 or 8 bytes), but that increase will be more than offset
by the next two patches.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>