Pull up following revision(s) (requested by bouyer in ticket #1399):

sys/external/bsd/ipf/netinet/fil.c: revision 1.31
sys/external/bsd/ipf/netinet/ip_fil_netbsd.c: revision 1.32
sys/external/bsd/ipf/netinet/ip_fil_netbsd.c: revision 1.33

Fix 2 bugs, reported by Edgar Fuss on tech-net@
- pfil_run_hooks() can be called recursively, so we have to
  #define FASTROUTE_RECURSION in fil.c
- ip6_if_output()/nd6_output() will free the mbuf on error, to make sure
  to set *mpp to NULL so the caller won't try to free it again.

fix double space in comment

(martin)