Currently, project quota could be changed by fssetxattr
ioctl, and existed permission check inode_owner_or_capable()
is obviously not enough, just think that common users could
change project id of file, that could make users to
break project quota easily.

This patch try to follow same regular of xfs project
quota:

"Project Quota ID state is only allowed to change from
within the init namespace. Enforce that restriction only
if we are trying to change the quota ID state.
Everything else is allowed in user namespaces."

Besides that, check and set project id'state should
be an atomic operation, protect whole operation with
inode lock.
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>