Kernel route syncer supports multiple tables.

The changes are just too extensive for lazy me to list them
there, but see the comment at the top of sysdep/unix/krt.c.
The code got a bit more ifdeffy than I'd like, though.

Also fixed a bunch of FIXME's and added a couple of others. :)

sysdep/linux/netlink/krt-scan.h

@@ -17,6 +17,7 @@
 
 struct krt_scan_params {
   int async;				/* Allow asynchronous events */
+  int table_id;				/* Kernel table ID we sync with */
 };
 
 struct krt_scan_status {