i40e: Fix static checker warning

This patch fixes the following static checker warning:

  drivers/net/ethernet/intel/i40e/i40e_dcb.c:342
  i40e_lldp_to_dcb_config() warn: 'tlv' can't be NULL.

Exit criteria from the while loop is encountering LLDP END
LV or if the TLV length goes beyond the buffer length.

Change-ID: I7548b16db90230ec2ba0fa791b0343ca8b7dd5bb
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Neerav Parikh <Neerav.Parikh@intel.com>
Acked-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Kevin Scott <kevin.c.scott@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Tested-By: Jack Morgan<jack.morgan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_dcb.c

@@ -332,22 +332,25 @@ i40e_status i40e_lldp_to_dcb_config(u8 *lldpmib,
 	u16 type;
 	u16 length;
 	u16 typelength;
+	u16 offset = 0;
 
 	if (!lldpmib || !dcbcfg)
 		return I40E_ERR_PARAM;
 
 	/* set to the start of LLDPDU */
 	lldpmib += ETH_HLEN;
 	tlv = (struct i40e_lldp_org_tlv *)lldpmib;
-	while (tlv) {
+	while (1) {
 		typelength = ntohs(tlv->typelength);
 		type = (u16)((typelength & I40E_LLDP_TLV_TYPE_MASK) >>
 			     I40E_LLDP_TLV_TYPE_SHIFT);
 		length = (u16)((typelength & I40E_LLDP_TLV_LEN_MASK) >>
 			       I40E_LLDP_TLV_LEN_SHIFT);
+		offset += sizeof(typelength) + length;
 
-		if (type == I40E_TLV_TYPE_END)
-			break;/* END TLV break out */
+		/* END TLV or beyond LLDPDU size */
+		if ((type == I40E_TLV_TYPE_END) || (offset > I40E_LLDPDU_SIZE))
+			break;
 
 		switch (type) {
 		case I40E_TLV_TYPE_ORG: