xfs: introduce protection for drop nlink

[ Upstream commit 2b99e410 ]

When abnormal drop_nlink are detected on the inode,
return error, to avoid corruption propagation.

Signed-off-by: Cheng Lin <cheng.lin130@zte.com.cn>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>