netxen: free napi resources during detach

o Defer napi resouce allocation to device attach.

o Free napi resources and delete napi during detach.

This ensures right behavior across firmware reset.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>