* gcm-aes.c (gcm_aes_set_iv): Use GCM_SET_IV.

(gcm_aes_set_key): Deleted cast.
(gcm_aes_encrypt): Likewise.
(gcm_aes_decrypt): Likewise.
(gcm_aes_digest): Likewise.
(gcm_aes_update): One less argument to GCM_UPDATE.

* gcm.h (GCM_SET_KEY): Added cast to nettle_crypt_func *. Help
compiler type checking despite this cast.
(GCM_ENCRYPT): Likewise.
(GCM_DECRYPT): Likewise.
(GCM_DIGEST): Likewise.
(GCM_SET_IV): New macro, for completeness.
(GCM_UPDATE): Deleted unused argument encrypt.

Rev: nettle/ChangeLog:1.156
Rev: nettle/gcm-aes.c:1.4
Rev: nettle/gcm.h:1.12