Handle Nodes changing IP address

[nieznanysprawiciel]

Why:

• When Node behind NAT connects to public Node, it's port will change from time to time, because routers can't track UDP connections (because UDP is connection-less). From public Node's perspective it looks like packet incoming from unknown address
• Current implementation probably sends Disconnected message, what breaks Session (and TCP connection as well). From GSB perspective this will cause timeout waiting for message to be sent.
• This affects especially Nodes that send occasional message after long period of inactivity (for example Invoice after exponentially growing period)

Acceptance criteria:

• In case of changing addresses, Session shouldn't be closed, but the same Session should be used
• NetworkView should be updated with new information
• NetworkView should distinguish list of private and public addresses
• Research if sending pings with higher frequency can prevent changing address on router
• Check if problem describe here: https://github.com/golemfactory/golem-internal/issues/627 was solved