bootpd: avoid the same error indication for different issues

There were several (apparently) copy-pasted NEED validation macros,
leading to the same error string for different issues. Change the
YP and NTP tags so they are distinct.

PR: 30863
Submitted by: Dan Lukes <dan@obluda.cz>
Reviewed by: markj
MFC after: 1 week
Event: Waterloo Hackathon 2019