geliboot: Use the correct IV length for AES-XTS.

[jhb]

Summary

• 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
Sponsored by: FreeBSD Foundation

[kevans]

Tag mikael, he might be able to test it.