gro: refetch inet6_protos[] after pulling ext headers

ipv6_gro_receive() doesn't update the protocol ops after pulling
the ext headers. It looks like a typo.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>