fou: Prevent unbounded recursion in GUE error handler also with UDP-Lite

fou: Prevent unbounded recursion in GUE error handler also with UDP-Lite

In commit 9552a5f13a10 ("fou: Prevent unbounded recursion in GUE error
handler"), I didn't take care of the case where UDP-Lite is encapsulated
into UDP or UDP-Lite with GUE. From a syzbot report about a possibly
similar issue with GUE on IPv6, I just realised the same thing might
happen with a UDP-Lite inner payload.

Also skip exception handling for inner UDP-Lite protocol.

Fixes: 9552a5f13a10 ("fou: Prevent unbounded recursion in GUE error handler")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>