[XFRM]: Fix ordering issue in xfrm_dst_hash_transfer().

Keep ordering of policy entries with same selector in
xfrm_dst_hash_transfer().

Issue should not appear in usual cases because multiple policy entries
with same selector are basically not allowed so far.  Bug was pointed
out by Sebastien Decugis <sdecugis@hongo.wide.ad.jp>.

We could convert bydst from hlist to list and use list_add_tail()
instead.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Acked-by: Sebastien Decugis <sdecugis@hongo.wide.ad.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>