- Use AES_XTS_IV_LEN instead of the key length as the IV length.
- Use G_ELI_IVKEYLEN as the size of the zeroed iv[] array in
  g_eli_crypto_cipher() to match geli_io().

PR:		261172
Reported by:	Malcolm Matalka <mmatalka@gmail.com>, mikael
Reviewed by:	markj
Sponsored by:	FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33884