IP connectivity metrics: add transport field.

This patch adds a transport field dimension to IpConnectivityEvent for
replacing interface name, and eventually network ids.

At the moment the transport field is not populated.

Test: manually taking a diff against reference ipconnectivity.proto
Bug: 32198976
Change-Id: Ia66cabda0b08076c87dc83c4f6ff98581f750884
1 file changed