wifi.proto: New Fields for Link Probe Metrics

Added new fields to store metrics for link probes.
Created standard protobuf message type for storing ranged histograms.

Bug: 112029045
Test: compiles, frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Change-Id: Iac041cbf87f8fa9b95d6d9cedba97c61410739dc