Flip the default for OPENSSL_KTLS to arm64

This is required to make use of KERN_TLS

Reviewed by: jhb
Sponsored by: Ampere Computing
Submitted by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D28405

(cherry picked from commit e6b7809cdfc4389d2fc1df2c7fdff08a4a110c77)