configitems: register the 'server.maxhttpheaderlen' config

mercurial/configitems.py

@@ -128,6 +128,9 b" coreconfigitem('server', 'concurrent-pus"
 coreconfigitem('server', 'disablefullbundle',
     default=False,
 )
+coreconfigitem('server', 'maxhttpheaderlen',
+    default=1024,
+)
 coreconfigitem('ui', 'clonebundleprefers',
     default=list,
 )

mercurial/wireproto.py

@@ -771,7 +771,7 b' def _capabilities(repo, proto):'
 
     if proto.name == 'http':
         caps.append('httpheader=%d' %
-                    repo.ui.configint('server', 'maxhttpheaderlen', 1024))
+                    repo.ui.configint('server', 'maxhttpheaderlen'))
         if repo.ui.configbool('experimental', 'httppostargs', False):
             caps.append('httppostargs')