LU-13805 obd: Reserve unaligned DIO connect flag

LU-13805 obd: Reserve unaligned DIO connect flag

Unaligned DIO generally requires only client changes, but
an assert must be removed from ZFS servers for it to work
correctly.  This means we need a connect flag to recognize
whether or not a server running ZFS can safely use
unaligned DIO.

All OSTs will present this flag - to keep things simple -
but if the flag is not present, we'll still do unaligned
DIO to ldiskfs OSTs.

Actual implementation will be in another patch, this one
just creates the flag itself.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I8b149cc54f4fb11e64182c65f2fbb01f8a3d3868
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51075
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>