sys_util: add size to mmap InvalidRange error
sys_util: add size to mmap InvalidRange error

The current error doesn't provide sufficient information to debug
InvalidRange errors; add the size of the region so that the bounds of
the comparison can be determined from the error message.

BUG=None
TEST=cargo test -p sys_util

Change-Id: I8e7fbd750ab84c43bbf0435230b7d3cf466783da
Signed-off-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1574964
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm