Make handler functions available in <SharedCode>

[gtarawneh]

Is it possible to add support for using handler_log and handler_exit in <SharedCode>?

[m8pple]

Shane would need to comment about the 0.3 softswitch, but for the older 0.2 softswitch I think
that it would probably already work. It uses a global context to track which device is active,
so there is not a problem there.

Supporting it in epoch_sim is a little more complex, though certainly not impossible.
At the moment the handler_log function is a lambda for convenience reasons, as it
stays within the scope of the handler. It could be forwarded out into global scope
using std::function or something, though it would need to be a thread-local-variable...

So yes, I think that can be supported with a small performance penalty in software,
and no performance penalty in HW. I'll talk to Shane about it to make sure it's still
possible though.