ipdb: pause when interface was moved to a netns
ipdb: set ipaddr only when link is set

IPv6 can be flushed from some interface types, when they change the state.
So, assign addresses only when the interface is set already.

+ force poll 'veth' for IP addresses.

Bug-Url: https://github.com/svinota/pyroute2/issues/84
tests: cover interface rename + IPv6 + flags for netns ops

Bug-Url: https://github.com/svinota/pyroute2/issues/84