address.proto: added doc for abstract sockets (#462)
address.proto: added doc for abstract sockets (#462)

Signed-off-by: Sylvain Mellak <33adf97b0da6841a55e95c8100dea97f2c97228e@google.com>

jrajahalme/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,lyft/envoy-api