net: blackhole_dev: fix build warning for ethh set but not used

lib/test_blackhole_dev.c sets a variable that is never read, causing
this following building warning:

	lib/test_blackhole_dev.c:32:17: warning: variable 'ethh' set but not used [-Wunused-but-set-variable]

Remove the variable struct ethhdr *ethh, which is unused.

Fixes: 509e56b ("blackhole_dev: add a selftest")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: leitao

lib/test_blackhole_dev.c

@@ -29,7 +29,6 @@ static int __init test_blackholedev_init(void)
 {
 	struct ipv6hdr *ip6h;
 	struct sk_buff *skb;
-	struct ethhdr *ethh;
 	struct udphdr *uh;
 	int data_len;
 	int ret;
@@ -61,7 +60,7 @@ static int __init test_blackholedev_init(void)
 	ip6h->saddr = in6addr_loopback;
 	ip6h->daddr = in6addr_loopback;
 	/* Ether */
-	ethh = (struct ethhdr *)skb_push(skb, sizeof(struct ethhdr));
+	skb_push(skb, sizeof(struct ethhdr));
 	skb_set_mac_header(skb, 0);
 
 	skb->protocol = htons(ETH_P_IPV6);