fix: acknowledge livereload_port from site config too (#9606)

Merge pull request 9606

docs/_data/config_options/serve.yml

@@ -34,6 +34,7 @@
 
 - name: Live reload port
   description: Port for LiveReload to listen on.
+  option: "livereload_port: PORT"
   flag: "--livereload-port PORT"
 
 

lib/jekyll/commands/serve.rb

@@ -71,7 +71,6 @@ module Jekyll
             end
 
             cmd.action do |_, opts|
-              opts["livereload_port"] ||= LIVERELOAD_PORT
               opts["serving"] = true
               opts["watch"]   = true unless opts.key?("watch")
 
@@ -94,6 +93,7 @@ module Jekyll
           opts = configuration_from_options(opts)
           destination = opts["destination"]
           if opts["livereload"]
+            opts["livereload_port"] ||= LIVERELOAD_PORT
             validate_options(opts)
             register_reload_hooks(opts)
           end