tree e74fe53229e661c2fd651be961f78fef55512374
parent e7c780d4e66839bf3e17a1ccd6574831c036e738
author chen xu <fionaxu@google.com> 1550780733 -0800
committer chen xu <fionaxu@google.com> 1550780864 -0800

fix issue that carrier id returns zero

if parent carrier is is not set, by default proto will assign 0 to it.
we should differentiate unset and treat it as unknown carrier id.

Bug: 124770250
Test: Manual test
Change-Id: I991ce1128af47d114f9eeabf1e7c2ef426945857