bridge: fix IPv6 queries for bridge multicast snooping

This patch fixes a missing ntohs() for bridge IPv6 multicast snooping.

Signed-off-by: David L Stevens <dlstevens@us.ibm.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>