ctdbd: Make the link status of new interfaces more flexible

ctdbd: Make the link status of new interfaces more flexible

Neither up nor down is a good default value for the link status of a
new interface.  Up means that IPs can be assigned to interfaces before
the true state is known and they can move away quickly if the interface
is actually down.  Down means that IPs can't be assigned to an interface
for a variable amount of time - until a monitor cycle occurs - and this
can result in imbalanced IPs.

This is a neat compromise.  Before the startup event completes, IPs
can't be assigned to interfaces because all interfaces begin in a down
state.  As soon as the startup event completes, IPs can be allocated
to any interface that has been marked up by the eventscript.  Later,
during normal operation, newly added IPs can be assigned to new
interfaces immediately.  The IPs will still move away if an interface
is noticed to be down in the next monitor cycle, but that is the
exception rather than the rule.

Signed-off-by: Martin Schwenke <martin@meltin.net>
(This used to be ctdb commit 9275a69a414482f1053ae14528d5972575b9214e)