lib/nicbm: pointer to runner in device base class

All devices will somehow need this, might as well stick it in the base
class.

lib/simbricks/nicbm/nicbm.cc

@@ -475,6 +475,7 @@ void Runner::EventTrigger() {
 Runner::Runner(Device &dev) : dev_(dev), events_(EventCmp()) {
   // mac_addr = lrand48() & ~(3ULL << 46);
   dma_pending_ = 0;
+  dev_.runner_ = this;
 
   int rfd;
   if ((rfd = open("/dev/urandom", O_RDONLY)) < 0) {

lib/simbricks/nicbm/nicbm.h

@@ -63,6 +63,8 @@ class Runner {
  public:
   class Device {
    protected:
+    friend class Runner;
+    Runner *runner_;
     bool int_intx_en_;
     bool int_msi_en_;
     bool int_msix_en_;