When we release an ip, get the interface name from the kernel

When we release an ip, get the interface name from the kernel

instead of using the interface where ctdb thinks the ip is hosted at.
The difference is that this now allows us to handle cases where we want to release an ip   but ctdbd does not know which interface the ip is assigned on.
(user has used 'ip addr add...'  and manually assigned an ip to the wrong interface)

(This used to be ctdb commit c6bf22ba5c01001b7febed73dd16a03bd3fd2bed)