eal: tighten permissions on shared memory files

eal: tighten permissions on shared memory files

When creating files on disk, e.g. for EAL configuration or shared memory
locks, etc., there is no need to grant any permissions on those files to
other users. All directories are already created with 0700 permissions, so
we should create all files with 0600 permissions.

Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>