MINOR: trace: ensure -dt priority over traces config section

MINOR: trace: ensure -dt priority over traces config section

Traces can be activated on startup either via -dt command line argument
or via the traces configuration section. This can caused confusion as it
may not be clear as trace source can be completed or overriden by one or
the other.

Fix the precedence to give the priority to the command line argument.
Now, each trace source configured via -dt is first resetted to a default
state before applying new settings. Then, it is impossible to change a
trace source via the configuration file if it was already targetted via
-dt argument.