py3: use pycompat.strkwargs()

Otherwise we get an error attempting to dispatch a command with
arguments because we're passing a dict with bytes keys.

Differential Revision: https://phab.mercurial-scm.org/D4732

mercurial/wireprotov2server.py

@@ -339,7 +339,7 b' def dispatch(repo, proto, command):'
     func, spec = COMMANDS[command]
     args = proto.getargs(spec)
 
-    return func(repo, proto, **args)
+    return func(repo, proto, **pycompat.strkwargs(args))
 
 @interfaceutil.implementer(wireprototypes.baseprotocolhandler)
 class httpv2protocolhandler(object):