e1000e: Fix 82572EI that has no hardware timestamp support

With the Intel 82527EI (driver: e1000e) there is an issue when running
the ptpd2 program, that leads to a kernel oops.  The reason is here that
in e1000_xmit_frame() a work queue will be scheduled that has not been
initialized in this case.  The work queue "tx_hwstamp_work" will only be
initialized if adapter->flags & FLAG_HAS_HW_TIMESTAMP set.  This check
is missing in e1000_xmit_frame().

The following patch adds the missing check.
Signed-off-by: Mathias Koehrer <mathias.koehrer@etas.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -5636,8 +5636,9 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 	count = e1000_tx_map(tx_ring, skb, first, adapter->tx_fifo_limit,
 			     nr_frags);
 	if (count) {
-		if (unlikely((skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
-			     !adapter->tx_hwtstamp_skb)) {
+		if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
+		    (adapter->flags & FLAG_HAS_HW_TIMESTAMP) &&
+		    !adapter->tx_hwtstamp_skb) {
 			skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 			tx_flags |= E1000_TX_FLAGS_HWTSTAMP;
 			adapter->tx_hwtstamp_skb = skb_get(skb);