libxc: drop size parameter from xc_flask_context_to_sid()

Nul-terminated strings are passed in all cases, so the strlen() can very
well be invoked by the function itself. In preparation for a hypervisor
change also include the nul terminator in the size calculation.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -1754,7 +1754,7 @@ static PyObject *pyflask_context_to_sid(PyObject *self, PyObject *args,
         return PyErr_SetFromErrno(xc_error_obj);
     }
 
-    ret = xc_flask_context_to_sid(xc_handle, ctx, strlen(ctx), &sid);
+    ret = xc_flask_context_to_sid(xc_handle, ctx, &sid);
 
     xc_interface_close(xc_handle);