nfp: remove defensive checks around ndo_open()/ndo_close()

Device open and close handlers check if the device is already
in the desired state.  Thanks to our reconfig infrastructure
this should not be necessary, there doesn't seem to be any
code in the driver which depends on it.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>