nfp: reorder open and close functions

We will soon reuse parts of .ndo_stop() for clean up after errors
in .ndo_open().  Reorder the associated functions to make that possible.

No functional changes.

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