This patch adds FLUSHSA and FLUSHPOLICY to xfrm_user which are
analagous to SADB_FLUSH and SADB_X_SPDFLUSH in af_key.

This is useful in KMs on startup/shutdown so that the system is
reset to a known state.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@redhat.com>