Implement most prefixlen operations as OP_RANGE (prefixlen A - B).

Implement most prefixlen operations as OP_RANGE (prefixlen A - B).
Simplify the RDE logic this way and make it possible to load such ranges
into a much faster lookup trie for prefix-sets.
When printing the config bgpd tries to use the nices way to express the rule:
e.g.    match from any prefix 18.0.0.0/8 prefixlen 8 - 32
becomes match from any prefix 18.0.0.0/8 or-longer
Apart from that there is no user visible change because of this.
OK sthen@