nwfilter: fix deadlock caused updating network device and nwfilter
    
    Commit 6e5c79a1 tried to fix deadlock between nwfilter{Define,Undefine}
    and starting of guest, but this same deadlock exists for
    updating/attaching network device to domain.
    
    The deadlock was introduced by removing global QEMU driver lock because
    nwfilter was counting on this lock and ensure that all driver locks are
    locked inside of nwfilter{Define,Undefine}.
    
    This patch extends usage of virNWFilterReadLockFilterUpdates to prevent
    the deadlock for all possible paths in QEMU driver. LXC and UML drivers
    still have global lock.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1143780
    
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>