sun: Add SPDX license tags to Sun network drivers

Add the appropriate SPDX license tags to the Sun network drivers
as outlined in Documentation/process/license-rules.rst.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/sun/sungem.c b/drivers/net/ethernet/sun/sungem.c
index a7afcee..7a16d40 100644
--- a/drivers/net/ethernet/sun/sungem.c
+++ b/drivers/net/ethernet/sun/sungem.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* $Id: sungem.c,v 1.44.2.22 2002/03/13 01:18:12 davem Exp $
  * sungem.c: Sun GEM ethernet driver.
  *