app/testpmd: setup attached ports on probe event

app/testpmd: setup attached ports on probe event

After probing is done, each new port must be setup.
The new ports are currently guessed by iterating on ports
matching the devargs string used for probing.

When probing a port, it is possible that one more port probing
get triggered (e.g. PF is automatically probed when probing
a VF representor). Such automatic probing will be caught only on event.

The iterator loop may be replaced by a call from the event callback.
In order to be able to test both modes, a command is added
to choose between iterator and event modes.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>