We get a pointer to the ipv6 hdr in br_ip6_multicast_query but we may
call pskb_may_pull afterwards and end up using a stale pointer.
So use the header directly, it's just 1 place where it's needed.

Fixes: 08b202b6 ("bridge br_multicast: IPv6 MLD support.")
Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Tested-by: NMartin Weinelt <martin@linuxlounge.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>