struct socket has a 16 bit hole that triggers kmemcheck warnings.

As suggested by Ingo, use kmemcheck annotations
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>