= can: be more resilient against stray `Terminated` messages in HttpHostConnectionSlot, fixes #459

Accomplished by introducing a new state just for waiting for connection
termination.
Merge pull request #482 from jrudolph/i/459/fix-host-connector-not-expecting-connection-termination

= can: be more resilient against stray `Terminated` messages in HttpHostConnectionSlot, fixes #459