net: switch memcpy_fromiovec()/memcpy_fromiovecend() users to copy_from_iter()

That takes care of the majority of ->sendmsg() instances - most of them
via memcpy_to_msg() or assorted getfrag() callbacks.  One place where we
still keep memcpy_fromiovecend() is tipc - there we potentially read the
same data over and over; separate patch, that...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9a8bafe..b349c96 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2692,8 +2692,7 @@
 
 static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
 {
-	/* XXX: stripping const */
-	return memcpy_fromiovec(data, (struct iovec *)msg->msg_iter.iov, len);
+	return copy_from_iter(data, len, &msg->msg_iter) == len ? 0 : -EFAULT;
 }
 
 static inline int memcpy_to_msg(struct msghdr *msg, void *data, int len)