xfrm: xfrm_algo: correct usage of RIPEMD-160

This patch fixes the usage of RIPEMD-160 in xfrm_algo which in turn
allows hmac(rmd160) to be used as authentication mechanism in IPsec
ESP and AH (see RFC 2857).

Signed-off-by: Adrian-Ken Rueegsegger <rueegsegger@swiss-it.ch>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>