On Android, the system resolver can return IPv4 addresses as IPv6-mapped
addresses (i.e. `::ffff:a.b.c.d`). After the switch to `net/netip`
(19008a3), this case is no longer handled and a response like this will
be seen as failure to resolve any IPv4 addresses.
Handle this case by simply calling `Unmap()` on the returned IPs. Fixes#5698.
Signed-off-by: Peter Cai <peter@typeblog.net>
4597ec1037