There was inconsistency in which error codes would get accepted and ignored in the network manager unit test callbacks. Add following results, so we just detach the handle instead of causing assertion failure:
- ISC_R_SHUTTINGDOWN - when the network manager is shutting down
- ISC_R_CANCELED - the socket has been shut down
- ISC_R_EOF - the (TCP) communication has ended on the other side
- ISC_R_CONNECTIONRESET - the TCP connection was reset
This should fix some of the spurious unit test failures.
Closes #3601 (closed)