Try to make most routerstatus_t interfaces const

src/or/circuitbuild.c

src/or/control.c

src/or/control.h

src/or/directory.c

src/or/directory.h

src/or/dirserv.c

src/or/dirserv.h

src/or/networkstatus.c

src/or/networkstatus.h

src/or/nodelist.c

src/or/routerlist.c

src/or/routerlist.h