xfs: make inode64 as the default allocation mode

since 64-bit inodes can be accessed while using inode32, and these can
also be used on 32-bit kernels, there is no reason to still keep inode32
as the default mount option.  If the filesystem cannot handle 64bit
inode numbers (i.e CONFIG_LBDAF is not enabled and BITS_PER_LONG == 32),
XFS_MOUNT_SMALL_INUMS will still be set by default, so inode64 is not an
unconditional default value.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>