Define and use nettle_cipher_func, for block ciphers.

ChangeLog

aes128-meta.c

aes192-meta.c

aes256-meta.c

arctwo-meta.c

camellia128-meta.c

camellia192-meta.c

camellia256-meta.c

cast128-meta.c

cbc.c

cbc.h

ctr.c

ctr.h

des-compat.c

eax.c

eax.h

examples/nettle-benchmark.c

examples/nettle-openssl.c

gcm-aes.c

gcm.c