opentelemetry-otlp: Default the port correctly.

Current behavior uses http-proto port even when there's no desire to use
it.

Relates #1509

Author: hdost

opentelemetry-otlp/src/exporter/tonic/mod.rs

@@ -149,6 +149,7 @@ impl Default for TonicExporterBuilder {
         TonicExporterBuilder {
             exporter_config: ExportConfig {
                 protocol: crate::Protocol::Grpc,
+                endpoint: default_endpoint(crate::Protocol::Grpc),
                 ..Default::default()
             },
             tonic_config,