net: alteon: remove unused len variable

clang with W=1 reports
drivers/net/ethernet/alteon/acenic.c:2438:10: error: variable
  'len' set but not used [-Werror,-Wunused-but-set-variable]
                int i, len = 0;
                       ^
This variable is not used so remove it.
Signed-off-by: NTom Rix <trix@redhat.com>
Reviewed-by: NSimon Horman <simon.horman@corigine.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/alteon/acenic.c

@@ -2435,7 +2435,7 @@ static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
 	} else {
 		dma_addr_t mapping;
 		u32 vlan_tag = 0;
-		int i, len = 0;
+		int i;
 
 		mapping = ace_map_tx_skb(ap, skb, NULL, idx);
 		flagsize = (skb_headlen(skb) << 16);
@@ -2454,7 +2454,6 @@ static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
 			const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 			struct tx_ring_info *info;
 
-			len += skb_frag_size(frag);
 			info = ap->skb->tx_skbuff + idx;
 			desc = ap->tx_ring + idx;