inet: Decrease overhead of on-stack inet_cork.

When we fast path datagram sends to avoid locking by putting
the inet_cork on the stack we use up lots of space that isn't
necessary.

This is because inet_cork contains a "struct flowi" which isn't
used in these code paths.

Split inet_cork to two parts, "inet_cork" and "inet_cork_full".
Only the latter of which has the "struct flowi" and is what is
stored in inet_sock.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index e5e5425..ae64984 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -542,8 +542,8 @@
 		goto out;
 
 	offset = rp->offset;
-	total_len = inet_sk(sk)->cork.length - (skb_network_header(skb) -
-						skb->data);
+	total_len = inet_sk(sk)->cork.base.length - (skb_network_header(skb) -
+						     skb->data);
 	if (offset >= total_len - 1) {
 		err = -EINVAL;
 		ip6_flush_pending_frames(sk);