job_container/tmpfs: logic from container_p_create to its own function

In preparation for subsequent changes.

No functional change.

Bug 11093

src/plugins/job_container/tmpfs/job_container_tmpfs.c

@@ -318,7 +318,7 @@ static int _rm_data(const char *path, const struct stat *st_buf,
 	return 0;
 }
 
-extern int container_p_create(uint32_t job_id)
+static int _create_ns(uint32_t job_id)
 {
 	char job_mount[PATH_MAX];
 	char ns_holder[PATH_MAX];
@@ -558,6 +558,11 @@ exit2:
 	return rc;
 }
 
+extern int container_p_create(uint32_t job_id)
+{
+	return _create_ns(job_id);
+}
+
 /* Add a process to a job container, create the proctrack container to add */
 extern int container_p_join_external(uint32_t job_id)
 {