IsRoutable() doesn't exclude multicast (224.0.0.0/4, ff00::/8), so multicast addresses received over gossip can end up in addrman.
This adds IsMulticast() and excludes it in IsRoutable().
Test updates:
IsRoutable() excluded private, documentation, link-local and other
special ranges, but not multicast (224.0.0.0/4, ff00::/8). Gossiped
multicast addresses were therefore accepted into addrman and could be
selected for outbound connections.
Add CNetAddr::IsMulticast() and exclude it in IsRoutable().
addrman_getaddr generates addresses with every first octet, so the
expected counts drop by the multicast ones. The last asmap test vector
was an ff00::/8 address, which now maps to AS0 as unroutable; use a
non-multicast address at the top of the range instead (same AS).
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