Pull up following revision(s) (requested by ozaki-r in ticket #749):

sys/net/if.h: revision 1.259
sys/net/route.c: revision 1.209
sys/net/route.h: revision 1.118
sys/net/rtsock.c: revision 1.240

Resolve tangled lock dependencies in route.c

This change sweeps remaining lock decisions based on if locked or not by
moving utility functions of rtentry updates from rtsock.c and ensuring
holding the rt_lock.
It also improves the atomicity of a update of a rtentry.

(martin)