app/testpmd: fix crash when attaching a device

app/testpmd: fix crash when attaching a device

Below commit checks global device information to determine if a port uses
the softnic driver once initialized. Problem is that this information is
not available at this point when a port is initialized interactively
through a "port attach XXX" command, crashing testpmd.

This patch systematically initializes global device information to address
this issue.

Fixes: 5b590fbe09b6 ("app/testpmd: add traffic management forwarding mode")
Cc: stable@dpdk.org
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>