Updated netmap to new virtif interface

Updated netmap to new virtif interface.

Note: this needs the following patch to NetBSD source (rumpsrc) since if RUMP_VIF_LINKSTR is defined, sys/sockio.h must be included, since SIOC{G,S}LINKSTR are needed by the implementation; will submit this patch to NetBSD separately

```diff
diff --git a/sys/rump/net/lib/libvirtif/if_virt.c b/sys/rump/net/lib/libvirtif/i
index 2dd740c..465ed93 100644
--- a/sys/rump/net/lib/libvirtif/if_virt.c
+++ b/sys/rump/net/lib/libvirtif/if_virt.c
@@ -33,6 +33,9 @@ __KERNEL_RCSID(0, "$NetBSD: if_virt.c,v 1.47 2014/04/02 19:44:
 #include <sys/kmem.h>
 #include <sys/cprng.h>
 #include <sys/module.h>
+#ifdef RUMP_VIF_LINKSTR
+#include <sys/sockio.h>
+#endif
 
 #include <net/bpf.h>
 #include <net/if.h>
```