Fix k5tls module for OpenSSL 3

Fix k5tls module for OpenSSL 3

Starting in OpenSSL 3, connection termination without a close_notify
alert causes SSL_read() to return SSL_ERROR_SSL instead of
SSL_ERROR_SYSCALL.  OpenSSL 3 also provides a new option
SSL_OP_IGNORE_UNEXPECTED_EOF which allows an application to explicitly
ignore possible truncation attacks and receive SSL_ERROR_ZERO_RETURN
instead.

Remove the call to SSL_CTX_get_options() since SSL_CTX_set_options()
doesn't clear existing options.

[ghudson@mit.edu: edited commit message and comment]