This patch fixes error handling when setting realtime and extent size hint
flags via fcntl(XFS_IOC_FSSETXATTR).
It also makes XFS_XFLAG_RTINHERIT/XFS_XFLAG_EXTSZINHERIT and
XFS_XFLAG_REALTIME/XFS_XFLAG_EXTSIZE flags mutually exclusive. Currently 
both,
the realtime and extent hint flags could be set at the same time,
which is not how the code is designed to work and could cause unexpected
behavior.
The realtime extent size is taken either from the on disk xfs inode 
di_extsize
(if set to non zero) or from the supperblock sb_rextsize fields. The parent
directory inheritance didn't inherit the di_extsize, which is also fixed in
this patch.

Regards,
Vlad