dlm_controld: bind to all interfaces for failover
    
    Support for automatic failover in the face of network interruptions
    is being added to the DLM kernel component. [1] This patch aids in that
    effort by adding a mechanism whereby userspace can convey to the
    kernel its intention to use all network addresses for automatic
    failover.  DLM's current default behavior is to bind to only a single
    interface.
    
    When --bind_all is set, dlm_controld will write to a configfs
    node that alerts the kernel of its intention to use all local network
    addresses for automatic failover. When selecting the next address to
    bind to, DLM will iterate through its list of local network addresses
    in a round-robin fashion.  Support for other address selection
    heuritics may be added in the future.
    
    It is important to understand that, per the DLM spec, while DLM
    can use a set of addresses for automatic failover, only one address
    is considered the active address between two DLM nodes at a time.
    This patch does not violate that constraint.
    
    [1] https://www.redhat.com/archives/cluster-devel/2019-January/msg00009.html
    
    Signed-off-by: David Windsor <dwindsor@redhat.com>