[Android] Increase the open files limit

As Crosswalk uses in-process mode, that's easier than Chromium
to reach the default limit(1024) of open files per process on
Android. So increase the limit to 4096 explicitly.

BUG=XWALK-2655
Merge pull request #2499 from xingnan/increase-open-files-limit

[Android] Increase the open files limit