LU-15404 ldiskfs: port truncate fix to Ubuntu 20 HWE

LU-15404 ldiskfs: port truncate fix to Ubuntu 20 HWE

A fixed landed for the LU-15404 bug which a truncate vs setxattr
race caused a kernel crash. This fix wasn't added in for new
Ubuntu 20 HWE kernels and the 5.10 kernel.

Change-Id: I43b33cd28335d1bc5796aa6651ecf847b4ea24e6
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/46480
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>