ioctl_userfaultfd.2: wfix

Hi,

Patch as attached. I think the comment on the variables in the struct is
reversed.

Thanks!

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/ioctl_userfaultfd.2

@@ -421,8 +421,8 @@ structure pointed to by
 .in +4n
 .EX
 struct uffdio_copy {
-    __u64 dst;    /* Source of copy */
-    __u64 src;    /* Destination of copy */
+    __u64 dst;    /* Destination of copy */
+    __u64 src;    /* Source of copy */
     __u64 len;    /* Number of bytes to copy */
     __u64 mode;   /* Flags controlling behavior of copy */
     __s64 copy;   /* Number of bytes copied, or negated error */