ROA entires are allowing to define a prefix with a maxlen.

ROA entires are allowing to define a prefix with a maxlen.
In the end this is just another way to specify a prefixlen range
and kind of an or-longer case with an upper limit.
So these two prefix statements are equivalent:
       prefix 10.0.0.0/8 prefixlen 8 - 24
       prefix 10.0.0.0/8 maxlen 24
While there also make 'prefixlen = 17' a OP_RANGE and because of that also
usable in prefix-set tables. Finally adjust printconf.c for those to
changes to print them nicely.
OK phessler@