bundle2: fix configuration name mismatch

During pulls bundle2 was checking server.bundle2, but during pushes it was
checking experimental.bundle2. This makes them both experimental.bundle2.

mercurial/exchange.py

@@ -537,7 +537,7 b' def pull(repo, remote, heads=None, force'
     lock = pullop.repo.lock()
     try:
         _pulldiscovery(pullop)
-        if (pullop.repo.ui.configbool('server', 'bundle2', False)
+        if (pullop.repo.ui.configbool('experimental', 'bundle2-exp', False)
             and pullop.remote.capable('bundle2-exp')):
             _pullbundle2(pullop)
         if 'changegroup' in pullop.todosteps: