net: Fix typo in net/core/sock.c.

In sock_queue_rcv_skb()  (net/core/sock.c) it should be:
"Cast sk->rcvbuf ..." instead of: "Cast skb->rcvbuf ..."

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>