enic: bug fix: check for zero port MTU before posting warning

Nic firmware can return zero for port MTU, so check for non-zero value
before checking for change in port MTU.

Signed-off-by: Scott Feldman <scofeldm@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/enic/enic_main.c b/drivers/net/enic/enic_main.c
index e0bf224..f800218 100644
--- a/drivers/net/enic/enic_main.c
+++ b/drivers/net/enic/enic_main.c
@@ -362,7 +362,7 @@
 {
 	u32 mtu = vnic_dev_mtu(enic->vdev);
 
-	if (mtu != enic->port_mtu) {
+	if (mtu && mtu != enic->port_mtu) {
 		if (mtu < enic->netdev->mtu)
 			printk(KERN_WARNING PFX
 				"%s: interface MTU (%d) set higher "