app/testpmd: align behaviour of multi-port detach

app/testpmd: align behaviour of multi-port detach

A port can be closed in multiple situations:
	- close command calling close_port() -> rte_eth_dev_close()
	- exit calling close_port() -> rte_eth_dev_close()
	- hotplug calling close_port() -> rte_eth_dev_close()
	- hotplug calling detach_device() -> rte_dev_remove()
	- port detach command, detach_device() -> rte_dev_remove()
	- device detach command, detach_devargs() -> rte_eal_hotplug_remove()

The flow rules are flushed before each close.
It was already done in close_port(), detach_devargs() and
detach_port_device() which calls detach_device(),
but not in detach_device(). As a consequence, it was missing for siblings
of port detach command and unplugged device.
The check before calling port_flow_flush() is moved inside the function.

The state of the port to close is checked to be stopped.
As above, this check was missing in detach_device(),
impacting the cases of a multi-port device unplugged or detached
with the port detach command.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>