Temporarily open BPF maps with no access flags.

Some device kernels have not yet picked up the commit that adds
support for BPF file open flags. Make userspace always use 0
until the kernels are fixed.

Also fix the log tag (it's currently empty).

Bug: 30950746
Test: "adb shell dumpsys netstats detail" returns data on device with 4.9 kernel
Change-Id: Icbab37e0bc9376d2c23e70eaa290a367bc804498