ice: set tx_tstamps when creating new Tx rings via ethtool

When the user changes the number of queues via ethtool, the driver
allocates new rings. This allocation did not initialize tx_tstamps. This
results in the tx_tstamps field being zero (due to kcalloc allocation), and
would result in a NULL pointer dereference when attempting a transmit
timestamp on the new ring.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>