stream-ssl: Avoid access-after-free error in update_ssl_config().
Commit
b84f503d "stream-ssl: Read existing CA certificate more eagerly
during bootstrap" inadvertently introduced an access-after-free error:
do_ca_cert_bootstrap() calls
stream_ssl_set_ca_cert_file(ca_cert.file_name, true), which calls
update_ssl_config(&ca_cert, file_name), which calls
free(ca_cert.file_name) then xstrdup(ca_cert.file_name).
Fix the problem.
Reported-by: Cedric Hobbs <cedric@nicira.com>
Reported-by: Peter Balland <peter@nicira.com>