net: set tb->fast_sk_family

We need to set the tb->fast_sk_family properly so we can use the proper
comparison function for all subsequent reuseport bind requests.

Fixes: 637bc8bb

 ("inet: reset tb->fastreuseport when adding a reuseport sk")
Reported-and-tested-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>