doc: add documentation for the defaultPort option

doc/api/http.md

@@ -1969,41 +1969,44 @@ changes:
 
 * `url` {string | URL}
 * `options` {Object}
-  * `protocol` {string} Protocol to use. **Default:** `'http:'`.
+  * `agent` {http.Agent | boolean} Controls [`Agent`][] behavior. Possible
+    values:
+    * `undefined` (default): use [`http.globalAgent`][] for this host and port.
+    * `Agent` object: explicitly use the passed in `Agent`.
+    * `false`: causes a new `Agent` with default values to be used.
+  * `auth` {string} Basic authentication i.e. `'user:password'` to compute an
+    Authorization header.
+  * `createConnection` {Function} A function that produces a socket/stream to
+    use for the request when the `agent` option is not used. This can be used to
+    avoid creating a custom `Agent` class just to override the default
+    `createConnection` function. See [`agent.createConnection()`][] for more
+    details. Any [`Duplex`][] stream is a valid return value.
+  * `defaultPort` {number} Default port for the protocol. **Default:**
+    `agent.defaultPort` if an `Agent` is used, else `undefined`.
+  * `family` {number} IP address family to use when resolving `host` or
+    `hostname`. Valid values are `4` or `6`. When unspecified, both IP v4 and
+    v6 will be used.
+  * `headers` {Object} An object containing request headers.
   * `host` {string} A domain name or IP address of the server to issue the
     request to. **Default:** `'localhost'`.
   * `hostname` {string} Alias for `host`. To support [`url.parse()`][],
     `hostname` will be used if both `host` and `hostname` are specified.
-  * `family` {number} IP address family to use when resolving `host` or
-    `hostname`. Valid values are `4` or `6`. When unspecified, both IP v4 and
-    v6 will be used.
-  * `port` {number} Port of remote server. **Default:** `80`.
   * `localAddress` {string} Local interface to bind for network connections.
-  * `socketPath` {string} Unix Domain Socket (cannot be used if one of `host`
-     or `port` is specified, those specify a TCP Socket).
   * `method` {string} A string specifying the HTTP request method. **Default:**
     `'GET'`.
   * `path` {string} Request path. Should include query string if any.
     E.G. `'/index.html?page=12'`. An exception is thrown when the request path
     contains illegal characters. Currently, only spaces are rejected but that
     may change in the future. **Default:** `'/'`.
-  * `headers` {Object} An object containing request headers.
-  * `auth` {string} Basic authentication i.e. `'user:password'` to compute an
-    Authorization header.
-  * `agent` {http.Agent | boolean} Controls [`Agent`][] behavior. Possible
-    values:
-    * `undefined` (default): use [`http.globalAgent`][] for this host and port.
-    * `Agent` object: explicitly use the passed in `Agent`.
-    * `false`: causes a new `Agent` with default values to be used.
-  * `createConnection` {Function} A function that produces a socket/stream to
-    use for the request when the `agent` option is not used. This can be used to
-    avoid creating a custom `Agent` class just to override the default
-    `createConnection` function. See [`agent.createConnection()`][] for more
-    details. Any [`Duplex`][] stream is a valid return value.
-  * `timeout` {number}: A number specifying the socket timeout in milliseconds.
-    This will set the timeout before the socket is connected.
+  * `port` {number} Port of remote server. **Default:** `defaultPort` if set,
+    else `80`.
+  * `protocol` {string} Protocol to use. **Default:** `'http:'`.
   * `setHost` {boolean}: Specifies whether or not to automatically add the
     `Host` header. Defaults to `true`.
+  * `socketPath` {string} Unix Domain Socket (cannot be used if one of `host`
+     or `port` is specified, those specify a TCP Socket).
+  * `timeout` {number}: A number specifying the socket timeout in milliseconds.
+    This will set the timeout before the socket is connected.
 * `callback` {Function}
 * Returns: {http.ClientRequest}