ipv6: xfrm: Handle errors reported by xfrm6_find_1stfragopt()

commit 6e80ac5cc992ab6256c3dae87f7e57db15e1a58c upstream.

xfrm6_find_1stfragopt() may now return an error code and we must
not treat it as a length.

Fixes: 2423496af35d ("ipv6: Prevent overrun when parsing v6 header options")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Acked-by: Craig Gallek <kraig@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/ipv6/xfrm6_mode_ro.c
Simple merge

diff --cc net/ipv6/xfrm6_mode_transport.c
Simple merge