net: ipv6: stop checking crypto_ahash_alignmask

Now that the alignmask for ahash and shash algorithms is always 0,
crypto_ahash_alignmask() always returns 0 and will be removed.  In
preparation for this, stop checking crypto_ahash_alignmask() in ah6.c.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>