inetpeer: Use correct AVL tree base pointer in inet_getpeer().

Family was hard-coded to AF_INET but should be daddr->family.

This fixes crashes when unlinking ipv6 peer entries, since the
unlink code was looking up the base pointer properly.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>