put iov_iter into msghdr

Note that the code _using_ ->msg_iter at that point will be very
unhappy with anything other than unshifted iovec-backed iov_iter.
We still need to convert users to proper primitives.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index cdedcf1..b50861b 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -755,11 +755,13 @@
 	struct msghdr *msg = from;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL) {
-		if (memcpy_fromiovecend(to, msg->msg_iov, offset, len) < 0)
+		/* XXX: stripping const */
+		if (memcpy_fromiovecend(to, (struct iovec *)msg->msg_iter.iov, offset, len) < 0)
 			return -EFAULT;
 	} else {
 		__wsum csum = 0;
-		if (csum_partial_copy_fromiovecend(to, msg->msg_iov, offset, len, &csum) < 0)
+		/* XXX: stripping const */
+		if (csum_partial_copy_fromiovecend(to, (struct iovec *)msg->msg_iter.iov, offset, len, &csum) < 0)
 			return -EFAULT;
 		skb->csum = csum_block_add(skb->csum, csum, odd);
 	}