ApfCounterTracker - reserve three slots for APFv6 endianness and allocate/transmit failure Technically only needed for APFv6+, but easier to always reserve. See also: aosp/2930730 Test: TreeHugger Signed-off-by: Maciej Żenczykowski <maze@google.com> Change-Id: I32515c9d3b9126f1b1e74d3f64d97facf3e8bdcf