Make a failure in ktls_sendfile a syscall error

a failure in ktls_sendfile results in an error in ERR_LIB_SSL, but its
really a syscall error, since ktls_sendfile just maps to a call to the
sendfile syscall.  Encode it as such

Fixes #23722

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23723)