Modify part of the name parameter in shm_open in ltp.

[txy-21]

The name parameter of shm_open needs to start with a forward slash: The operation of shm_open() is analogous to that of open(2). name specifies the shared memory object to be created or opened. For porta‐ ble use, a shared memory object should be identified by a name of the form /somename; that is, a null-terminated string of up to NAME_MAX (i.e., 255) characters consisting of an initial slash, followed by one or more characters, none of which are slashes.