e1000e: test for valid check_reset_block function pointer

commit 44abd5c12767a8c567dc4e45fd9aec3b13ca85e0 introduced NULL pointer
dereferences when attempting to access the check_reset_block function
pointer on 8257x and 80003es2lan non-copper devices.

This fix should be applied back through 3.4.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/e1000e/ethtool.c b/drivers/net/ethernet/intel/e1000e/ethtool.c
index d863075..905e214 100644
--- a/drivers/net/ethernet/intel/e1000e/ethtool.c
+++ b/drivers/net/ethernet/intel/e1000e/ethtool.c
@@ -258,7 +258,8 @@
 	 * When SoL/IDER sessions are active, autoneg/speed/duplex
 	 * cannot be changed
 	 */
-	if (hw->phy.ops.check_reset_block(hw)) {
+	if (hw->phy.ops.check_reset_block &&
+	    hw->phy.ops.check_reset_block(hw)) {
 		e_err("Cannot change link characteristics when SoL/IDER is active.\n");
 		return -EINVAL;
 	}
@@ -1615,7 +1616,8 @@
 	 * PHY loopback cannot be performed if SoL/IDER
 	 * sessions are active
 	 */
-	if (hw->phy.ops.check_reset_block(hw)) {
+	if (hw->phy.ops.check_reset_block &&
+	    hw->phy.ops.check_reset_block(hw)) {
 		e_err("Cannot do PHY loopback test when SoL/IDER is active.\n");
 		*data = 0;
 		goto out;