ice: Fix inability to set channels when down

Currently the driver prevents a user from doing
modprobe ice
ethtool -L eth0 combined 5
ip link set eth0 up

The ethtool command fails, because the driver is checking to see if the
interface is down before allowing the get_channels to proceed (even for
a set_channels).

Remove this check and allow the user to configure the interface
before bringing it up, which is a much better usability case.

Fixes: 87324e74

 ("ice: Implement ethtool ops for channels")
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>