More changes to the kernel syncer.

o  Now compatible with filtering.
o  Learning of kernel routes supported only on CONFIG_SELF_CONSCIOUS
   systems (on the others it's impossible to get it semantically correct).
o  Learning now stores all of its routes in a separate fib and selects
   the ones the kernel really uses for forwarding packets.
o  Better treatment of CONFIG_AUTO_ROUTES ports.
o  Lots of internal changes.