1e649491b8567151270095fda3bce8faea394952 enabled KERN_TLS in
riscv/conf/GENERIC, but didn't enable OPENSSL_KTLS.
This passes all testcases in the sys/kern/ssl_sendfile suite and
fixes CI failures seen here:
https://ci.freebsd.org/job/FreeBSD-main-riscv64-test/16606/testReport/sys.kern/ssl_sendfile/
PR: 293810
Fixes: 1e649491b8567151270095fda3bce8faea394952