[IPSEC]: Use HMAC template and hash interface

This patch converts IPsec to use the new HMAC template.  The names of
existing simple digest algorithms may still be used to refer to their
HMAC composites.

The same structure can be used by other MACs such as AES-XCBC-MAC.

This patch also switches from the digest interface to hash.

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