xfrm: release dst_orig in case of error in xfrm_lookup()

xfrm: release dst_orig in case of error in xfrm_lookup()

dst_orig should be released on error. Function like __xfrm_route_forward()
expects that behavior.
Since a recent commit, xfrm_lookup() may also be called by xfrm_lookup_route(),
which expects the opposite.
Let's introduce a new flag (XFRM_LOOKUP_KEEP_DST_REF) to tell what should be
done in case of error.

Fixes: f92ee61982d("xfrm: Generate blackhole routes only from route lookup functions")
Signed-off-by: huaibin Wang <[email protected]>
Signed-off-by: Nicolas Dichtel <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>