Move TrafficStats tags for the network stack constants

As per API council feedback, these constants should live in
a place that is private to the network stack, only with a
range defined in system API.

Bug: 129433383
Test: m
Change-Id: I84a90f84a9af6fef4667ee4d512ebd0413222086
(cherry picked from commit 79a6330650ca04bd7a08afbd63f8016a3b30bc72)