*: Add infrastructure to support zapi interface callbacks

*: Add infrastructure to support zapi interface callbacks

Start the conversion to allow zapi interface callbacks to be
controlled like vrf creation/destruction/change callbacks.

This will allow us to consolidate control into the interface.c
instead of having each daemon read the stream and react accordingly.
This will hopefully reduce a bunch of cut-n-paste stuff

Create 4 new callback functions that will be controlled by
lib/if.c

create -> A upper level protocol receives an interface creation event
The ifp is brand spanking newly created in the system.
up -> A upper level protocol receives a interface up event
This means the interface is up and ready to go.
down -> A upper level protocol receives a interface down
destroy -> A upper level protocol receives a destroy event
This means to delete the pointers associated with it.

At this point this is just boilerplate setup for future commits.
There is no new functionality.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>