Add more locks and comments for TrafficController

Add additional comments for the locking design inside TrafficController
and include the cookieTagMap and uidCounterSetMap into lock protection
to make the TrafficController safer for concurrent access.

Bug: 130334320
Test: netd_unit_test
Change-Id: I9194cdea2449dcf9b62cf00eab4bee48c09e6c84
Merged-In: I9194cdea2449dcf9b62cf00eab4bee48c09e6c84
(cherry picked from commit f01f5307)