While checking port availability in bind() or listen(), we used only
bhash for all v4-mapped-v6 addresses.  But there is no good reason not
to use bhash2 for v4-mapped-v6 non-wildcard addresses.

Let's do it by returning true in inet_use_bhash2_on_bind().  Then, we
also need to add a test in inet_bind2_bucket_match_addr_any() so that
::ffff:X.X.X.X will match with 0.0.0.0.

Note that sk->sk_rcv_saddr is initialised for v4-mapped-v6 sk in
__inet6_bind().
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>