ipv6: Consolidate route lookup sequences.
Route lookups follow a general pattern in the ipv6 code wherein we first find the non-IPSEC route, potentially override the flow destination address due to ipv6 options settings, and then finally make an IPSEC search using either xfrm_lookup() or __xfrm_lookup(). __xfrm_lookup() is used when we want to generate a blackhole route if the key manager needs to resolve the IPSEC rules (in this case -EREMOTE is returned and the original 'dst' is left unchanged). Otherwise plain xfrm_lookup() is used and when asynchronous IPSEC resolution is necessary, we simply fail the lookup completely. All of these cases are encapsulated into two routines, ip6_dst_lookup_flow and ip6_sk_dst_lookup_flow. The latter of which handles unconnected UDP datagram sockets. Signed-off-by: David S. Miller <email@example.com>