[c-nsp] sh bgp ivp6 u .. longer-prefixes broken in 12.2(18)SXF4?

[Matyas Koszik]

Somehow this command outputs some really strange results... If any of the
first <length> bits are set in <network>, there're no matching routes,
otherwise it shows all of them. This is true for <network> <= 32, for 33
it shows only a subset of the networks - again, if any of the first 33 bits
are set I get nothing.
For example:
show bgp ipv6 unicast ::/32 longer-prefixes
 - dumps the whole table
show bgp ipv6 unicast 2000::/3 longer-prefixes
 - shows nothing

(This was observed on a sup2.)