[XFRM]: Algorithm lookup using .compat name

Installing an IPsec SA using old algorithm names (.compat) does not work
if the algorithm is not already loaded. When not using the PF_KEY
interface, algorithms are not preloaded in xfrm_probe_algs() and
installing a IPsec SA fails.

Signed-off-by: Martin Willi <martin@strongswan.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>