The FP_ identifiers referred to fingerprints, but they also applied
to address ranges. The router_status_t name invited confusion with
routerstasus_t. Fixes ticket 29826.
This is an automated commit, generated by this command:
./scripts/maint/rename_c_identifier.py \
router_status_t rtr_flags_t \
FP_INVALID RTR_INVALID \
FP_BADEXIT RTR_BADEXIT \
FP_REJECT RTR_REJECT