In this new representation for wildcarded addresses, there are no
longer any 'magic addresses': rather, "a.b c.d", "*.a.b c.d" and
"*.a.b *.c.d" are all represented by a mapping from "a.b" to "c.d". we
now distinguish them by setting bits in the addressmap_entry_t
structure, where src_wildcard is set if the source address had a
wildcard, and dst_wildcard is set if the target address had a
wildcard.

This lets the case where "*.a.b *.c.d" or "*.a.b c.d" remap the
address "a.b" get handled trivially, and lets us simplify and improve
the addressmap_match_superdomains implementation: we can now have it
run in O(parts of address) rather than O(entries in addressmap).