When the instances were able to use their own options, the userstacktrace
option was left hardcoded for the top level. This made the instance
userstacktrace option bascially into a nop, and will confuse users that set
it, but nothing happens (I was confused when it happened to me!)

Cc: stable@vger.kernel.org
Fixes: 16270145 ("tracing: Add trace options for core options to instances")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>