iavf: iavf_suspend(): take RTNL before netdev_lock()

Fix an obvious violation of lock ordering.
Jakub's [1] added netdev_lock() call that is wrong ordered wrt RTNL,
but the Fixes tag points to crit_lock being wrongly placed (by lockdep
standards).

Actual reason we got it wrong is dated back to critical section managed by
pure flag checks, which is with us since the very beginning.

[1] afc66498 ("eth: iavf: extend the netdev_lock usage")

Fixes: 5ac49f3c ("iavf: use mutexes for locking of critical sections")
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>