Renamed host_addr_equal() as host_addr_equiv().

The new host_addr_equal() checks for true equality betweeen host addreses and
is suitable for use (directly or rather indirectly) for hash table comparisons.

Indeed, for all hashed structures, two items that satisfy equal(a, b) MUST also
satisfy hash(a) = hash(b), which was broken with the older host_addr_equal()
since only equivalence was tested.
Made host_addr_equiv() a non-inlined routine since it references itself.