Implement the new virinterface functions

Implement the new virinterface functions

* src/driver.h: add new driver functions virDrvNumOfDefinedInterfaces
  and virDrvListDefinedInterfaces
* src/libvirt.c: implements the entry points, calling new driver
  functions
* qemud/remote.c qemud/remote_dispatch_args.h qemud/remote_protocol.[chx]
  qemud/remote_dispatch_prototypes.h qemud/remote_dispatch_ret.h
  qemud/remote_dispatch_table.h src/remote_internal.c: implement the
  client/server side of the RPC