trace: param: fix tp_printk option related with tp_printk_stop_on_boot

Kernel param "tp_printk_stop_on_boot" starts with "tp_printk" which is
the exact as the other kernel param "tp_printk".
In compile & build process, It may not guaranteed that
"tp_printk_stop_on_boot" always checked before "tp_printk".
(By swapping its __setup() macro order, it may not work as expected.)
Some kernel params which starts with other kernel params consider this
problem. See commit 745a600 ("um: console: Ignore console= option")
or init/do_mounts.c:45 (setup function of "ro" kernel param)

Kernel param "tp_printk" can be handled with its value(0 or off) or
it can be handled without its value. (maybe it won't effect anything)
Fix setup function to ignore when the "tp_printk" becomes prefix of
other kernel param.

Signed-off-by: JaeSang Yoo <jsyoo5b@gmail.com>

kernel/trace/trace.c

@@ -252,6 +252,8 @@ __setup("trace_clock=", set_trace_boot_clock);
 
 static int __init set_tracepoint_printk(char *str)
 {
+	if (*str == '_')
+		return 0
 	if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0))
 		tracepoint_printk = 1;
 	return 1;