Fix kernel version control for proc_dir_entry

[liamnesson0111]

The struct proc_dir_entry is used in the plugin linux_check_fop. The struct was defined in module.c only in kernel versions greater than 3.13, causing an error when running linux_check_fop on systems with older kernel versions. I noticed that this struct hasn't changed at all between kernel versions 3.10 and 3.13, so we can make this plugin support more versions with this fix. This change is relatively significant because many distributions are shipped with a 3.10.~ kernel (CentOS 7 and RHEL 7, among others).