Revert "Change OTLP/HTTP port from 4317 to 4318 (#1839)" (#1847)

Apparently there is new evidence that one port may work after all:
https://github.com/open-telemetry/opentelemetry-collector/pull/3765/files

This reverts commit cce1d5996873de38a68e05eafa4d5e224df9b8f1 until we have the final
decision about the ability to have a single port, see:

open-telemetry/opentelemetry-specification#1846 (comment)

specification/protocol/exporter.md

@@ -10,7 +10,7 @@ The following configuration options MUST be available to configure the OTLP expo
 
 | Configuration Option | Description                                                  | Default           | Env variable                                                 |
 | -------------------- | ------------------------------------------------------------ | ----------------- | ------------------------------------------------------------ |
-| Endpoint (OTLP/HTTP) | Target to which the exporter is going to send spans or metrics. The endpoint MUST be a valid URL with scheme (http or https) and host, and MAY contain a port and path. A scheme of https indicates a secure connection. When using `OTEL_EXPORTER_OTLP_ENDPOINT`, exporters SHOULD follow the collector convention of appending the version and signal to the path (e.g. `v1/traces` or `v1/metrics`), if not present already. The per-signal endpoint configuration options take precedence and can be used to override this behavior. See the [OTLP Specification][otlphttp-req] for more details. | `https://localhost:4318` | `OTEL_EXPORTER_OTLP_ENDPOINT` `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` `OTEL_EXPORTER_OTLP_METRICS_ENDPOINT` |
+| Endpoint (OTLP/HTTP) | Target to which the exporter is going to send spans or metrics. The endpoint MUST be a valid URL with scheme (http or https) and host, and MAY contain a port and path. A scheme of https indicates a secure connection. When using `OTEL_EXPORTER_OTLP_ENDPOINT`, exporters SHOULD follow the collector convention of appending the version and signal to the path (e.g. `v1/traces` or `v1/metrics`), if not present already. The per-signal endpoint configuration options take precedence and can be used to override this behavior. See the [OTLP Specification][otlphttp-req] for more details. | `https://localhost:4317` | `OTEL_EXPORTER_OTLP_ENDPOINT` `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` `OTEL_EXPORTER_OTLP_METRICS_ENDPOINT` |
 | Endpoint (OTLP/gRPC) | Target to which the exporter is going to send spans or metrics. The endpoint SHOULD accept any form allowed by the underlying gRPC client implementation. Additionally, the endpoint MUST accept a URL with a scheme of either `http` or `https`. A scheme of `https` indicates a secure connection and takes precedence over the `insecure` configuration setting. If the gRPC client implementation does not support an endpoint with a scheme of `http` or `https` then the endpoint SHOULD be transformed to the most sensible format for that implementation. | `https://localhost:4317` | `OTEL_EXPORTER_OTLP_ENDPOINT` `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` `OTEL_EXPORTER_OTLP_METRICS_ENDPOINT` |
 | Insecure             | Whether to enable client transport security for the exporter's gRPC connection. This option only applies to OTLP/gRPC - OTLP/HTTP always uses the scheme provided for the `endpoint`. Implementations MAY choose to not implement the `insecure` option if it is not required or supported by the underlying gRPC client implementation. | `false` | `OTEL_EXPORTER_OTLP_INSECURE` `OTEL_EXPORTER_OTLP_SPAN_INSECURE` `OTEL_EXPORTER_OTLP_METRIC_INSECURE` |
 | Certificate File     | The trusted certificate to use when verifying a server's TLS credentials. Should only be used for a secure connection. | n/a               | `OTEL_EXPORTER_OTLP_CERTIFICATE` `OTEL_EXPORTER_OTLP_TRACES_CERTIFICATE` `OTEL_EXPORTER_OTLP_METRICS_CERTIFICATE` |

specification/protocol/otlp.md

@@ -473,7 +473,7 @@ connections SHOULD be configurable.
 
 #### OTLP/HTTP Default Port
 
-The default network port for OTLP/HTTP is 4318.
+The default network port for OTLP/HTTP is 4317.
 
 ## Implementation Recommendations