EX-8270 sptlrpc: don't crash for too-large chunk size

EX-8270 sptlrpc: don't crash for too-large chunk size

If the chunk size is too large, don't fall off the
end of the page_pool[] array with a large "order".

Test-Parameters: trivial
Fixes: d945f1b064 ("EX-6261 ptlrpc: extend sec bulk functionality")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I192ac1b227f1cab8405f6657e754101d353ebbe5
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53044
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>