Adjust crypto_apply function callbacks for OCF.

• crypto_apply() is only used for reading a buffer to compute a digest, so change the data pointer to a const pointer.

• To better match m_apply(), change the data pointer type to void * and the length from uint16_t to u_int. The length field in particular matters as none of the apply logic was splitting requests larger than UINT16_MAX.

• Adjust the auth_xform Update callback to match the function prototype passed to crypto_apply() and crypto_apply_buf(). This removes the needs for casts when using the Update callback.

• Change the Reinit and Setkey callbacks to also use a u_int length instead of uint16_t.

• Update auth transforms for the changes. While here, use C99 initializers for auth_hash structures and avoid casts on callbacks.

Reviewed by: cem
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D25171