Turned out that applications like ifconfig do not handle the change.
So revert ifa_flag format back to 2-letter hex value.
Introduced by:
commit 
479840ffdbe4242e8a25349218c8e0859223aa35
    "ipv6 addrconf: extend ifa_flags to u32"
Reported-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Tested-by: FLorent Fourcot <florent.fourcot@enst-bretagne.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
 static int if6_seq_show(struct seq_file *seq, void *v)
 {
        struct inet6_ifaddr *ifp = (struct inet6_ifaddr *)v;
-       seq_printf(seq, "%pi6 %02x %02x %02x %03x %8s\n",
+       seq_printf(seq, "%pi6 %02x %02x %02x %02x %8s\n",
                   &ifp->addr,
                   ifp->idev->dev->ifindex,
                   ifp->prefix_len,
                   ifp->scope,
-                  ifp->flags,
+                  (u8) ifp->flags,
                   ifp->idev->dev->name);
        return 0;
 }