LU-11787 test: Fix checkfilemap tests for 64K page

LU-11787 test: Fix checkfilemap tests for 64K page

File mapping is page size aligned. Modify the tests to handle 64K
page.

Lustre-change: https://review.whamcloud.com/45629
Lustre-commit: 7c88dfd28b5cc6114a85f187ecb2473657d42c9d

Test-Parameters: trivial clientdistro=el8.7 clientarch=aarch64 testlist=sanityn env=ONLY="71a 71b"
Change-Id: I316a197db8cdd0f9064431f8c572b43adf6110b8
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51287
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>