[IPSEC]: Move output replay code into xfrm_output

The replay counter is one of only two remaining things in the output code
that requires a lock on the xfrm state (the other being the crypto).  This
patch moves it into the generic xfrm_output so we can remove the lock from
the transforms themselves.

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