xfrm: Prepare for CRYPTO_MAX_ALG_NAME expansion

This patch fixes the xfrm_user code to use the actual array size
rather than the hard-coded CRYPTO_MAX_ALG_NAME length.  This is
because the array size is fixed at 64 bytes while we want to increase
the in-kernel CRYPTO_MAX_ALG_NAME value.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>