remoteDispatchAuthPolkit: Fix lock ordering deadlock if client closes connection...

remoteDispatchAuthPolkit: Fix lock ordering deadlock if client closes connection during auth

Locks in following text:
A: virNetServer
B: virNetServerClient
C: daemonClientPrivate

'virNetServerSetClientAuthenticated' locks A then B

'remoteDispatchAuthPolkit' calls 'virNetServerSetClientAuthenticated'
while holding C.

If a client closes its connection 'virNetServerProcessClients' with the
lock A and B locked will call 'virNetServerClientCloseLocked' which will
try to dispose of the 'client' private data by:

  ref(b);
  unlock(b);
  remoteClientFreePrivateCallbacks();
  lock(b);
  unref(b);

Unfortunately remoteClientFreePrivateCallbacks() tries lock C.

Thus the locks are held in the following order:

 polkit auth: C -> A
 connection close: A -> C

causing a textbook-example deadlock. To resolve it we can simply drop
lock 'C' before calling 'virNetServerSetClientAuthenticated' as the lock
is not needed any more.

Resolves: https://issues.redhat.com/browse/RHEL-20337
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>