Convert ipfilter to use new routing API.
Compile tested only.
Rename ip_sendmbuf to fib4_sendmbuf() and move it to rt_nhops api.
Convert IPv4 SAS to use new routing api.
Convert inp_lookup_mcast_ifp() to new routing api.
Add new fib4_lookup_nh_extended() which fills in nhop4_extended
 structure without doinf L2 resolve. It also requires freeing
 references by calling fib4_free_nh_ext().

Convert in_pcbladdr() to use it.
Convert tcp_maxmtu() to use it.
Convert all ip_rtaddr() users to fib4_lookup_nh_extended().
Remove ip_rtaddr().
Convert arpinput() to use new routing api.
Convert last piece of ip_forward to use new rouing api.
Convert ip_fastfwd() to use new routing api.
* Increase nh_flags to be u16 thus reducing nhop payload to be 48 bytes
* Use NHF_ namespace for all nhop flags
* Rename nhop_data -> nhop_prepend
* Rename fib4_lookup_nh_extended -> fib4_lookup_nh_ext
* Add "flags" argument to fib4_lookup_nh_ext() to specify whether we want
  returned nh_ext structure to be refcounted or not.
* Convert TOE framework to use new routing api.
* Add fib6_lookup_nh_ext().
* Rename union structures:
  nhop64_basic -> nhopu_basic,
  nhop64_extended -> nhopu_extended
Convert last piece of pf to use fib4_lookup_nh_ext().
Convert ofed to use new routing api.
Convert several places inside netinet6/ to new api.