netxen: protect device reset by rtnl_lock

o To prevent race conditions with other reset events.
  During suspend/resume and firmware recovery, acquire rtnl_lock,
  while changing interface state.

Acked-by: Dhananjay Phadke <dhananjay.phadke@qlogic.com>
Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>