Support for [immediate] callbacks in the zero copy API
Currently, in SMP mode, the zero copy API forwards all callbacks to their 'srcPe' via ckcallbackgroup, but this assumes the callback is meant to run on a worker thread, which isn't true of [immediate] methods of Node Groups. The zero copy API just needs to check the _entryTable and invoke the callback directly if it is immediate.
This patch added support for CkCallback's to [immediate] methods: https://charm.cs.illinois.edu/gerrit/#/c/charm/+/4196/
- Status changed from New to Implemented
Add an [immediate] callback zero copy API example: https://charm.cs.illinois.edu/gerrit/#/c/charm/+/4656/