LU-15933 libcfs: fix configure check for iov_iter member

LU-15933 libcfs: fix configure check for iov_iter member

Kernel commit v5.13-rc1-12-g8cd54c1c8480 changed iov_iter member
->type to ->iter_type, add check at configure to cover this change.

Lustre-change: https://review.whamcloud.com/47601
Lustre-commit: TBD (from f6bce444082d44d3dec9db00bce63dc92092c927)

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I8da26e1f6c6242a3260b458770ec34a65aecaf7d
Reviewed-on: https://review.whamcloud.com/47603
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>