ice: Fix to change Rx/Tx ring descriptor size via ethtool with DCBx

This patch fixes the call trace caused by the kernel when the Rx/Tx
descriptor size change request is initiated via ethtool when DCB is
configured. ice_set_ringparam() should use vsi->num_txq instead of
vsi->alloc_txq as it represents the queues that are enabled in the
driver when DCB is enabled/disabled. Otherwise, queue index being
used can go out of range.

For example, when vsi->alloc_txq has 104 queues and with 3 TCS enabled
via DCB, each TC gets 34 queues, vsi->num_txq will be 102 and only 102
queues will be enabled.

Signed-off-by: Usha Ketineni <usha.k.ketineni@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>