route(8): clarify -prefixlen description
Try to reword -prefixlen section to more clearly and accurately describe
how the -prefixlen modifier works.
While here, fix a word that igor considered a typo: aggregatable addresses
is a valid technical term per RFC-2374, but it was superseded by the
technical term "aggregator" in RFC-3587.
(I couldn't figure out where in the code the -prefixlen 64/aggregator part
was enforced, only the number 128, for the max prefixlen. I could use some
help tracking down where the value, 64, is enforced.)
MFC after: 1 week