LU-13479 kernel: only enable integrity metadata for reads and writes

LU-13479 kernel: only enable integrity metadata for reads and writes

We should not enable integrity for discard bio, it will fail the
integrity allocation and the discard bio will end with EIO.

Linux-commit: e69f18f06b97ed29645d020500222bfcec2b42b2

Test-Parameters: trivial clientdistro=el7.8 serverdistro=el7.8

Change-Id: I1fc9c6c7a6c53a6287466927ecfbb9af1f2a8f27
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/38324
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>