Tune "Failed to decapsulate incoming packet" log

[jamilbk]

These are always WARN, but in some cases they're expected:

• Client roams networks with an active DNS resource (e.g. GitHub.com). The Resource may continue sending packets to the Client but there is no valid IP mapping to receive them through and in most cases a new mapping has already been established
• Client ICE agent expires or dies before it can send InvalidateCandidate Message to its peer.

Tech-savvy users will be confused by the WARN logs -- perhaps they should be DEBUG in certain cases.