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
Merged-In: I4882686a86e7c6d42f4b0619b921d02619ed6d4c
Merged-In: I9b648ed6c687d56db61a54570c7880c51c1bae51