Defines starting with `n' in bsd/netat

• NBP_DEBUG bsd/netat/ddp_nbp.c:67
• NDEFERS bsd/netat/ddp_lap.c:128
• NROUTERS2TRAK bsd/netat/ddp_rtmp.c:63
• NULL_PNVESTR bsd/netat/ddp_nbp.c:1618
• NVE_LOCK bsd/netat/ddp_nbp.c:94