crypto: des3_ede - permit weak keys unless REQ_WEAK_KEY set

While its a slightly insane to bypass the key1 == key2 ||
key2 == key3 check in triple-des, since it reduces it to the
same strength as des, some folks do need to do this from time
to time for backwards compatibility with des.

My own case is FIPS CAVS test vectors. Many triple-des test
vectors use a single key, replicated 3x. In order to get the
expected results, des3_ede_setkey() needs to only reject weak
keys if the CRYPTO_TFM_REQ_WEAK_KEY flag is set.

Also sets a more appropriate RES flag when a weak key is found.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>