udp6: fix udp6_ehashfn() typo

Amit Klein reported that udp6_ehash_secret was initialized but never used.

Fixes: 1bbdceef ("inet: convert inet_ehash_secret and ipv6_hash_secret to net_get_random_once")
Reported-by: Amit Klein <aksecurity@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: David Ahern <dsahern@kernel.org>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>