net: mana: Allow setting the number of queues while the NIC is down

The existing code doesn't allow setting the number of queues while the
NIC is down.

Update the ethtool handler functions to support setting the number of
queues while the NIC is at down state.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>