drivers:net: Remove unnecessary OOM messages after netdev_alloc_skb

Emitting netdev_alloc_skb and netdev_alloc_skb_ip_align OOM
messages is unnecessary as there is already a dump_stack
after allocation failures.

Other trivial changes around these removals:

Convert a few comparisons of pointer to 0 to !pointer.
Change flow to remove unnecessary label.
Remove now unused variable.
Hoist assignment from if.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_selftest.c b/drivers/net/ethernet/mellanox/mlx4/en_selftest.c
index 3488c6d..2448f0d 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_selftest.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_selftest.c
@@ -58,10 +58,9 @@
 
 	/* build the pkt before xmit */
 	skb = netdev_alloc_skb(priv->dev, MLX4_LOOPBACK_TEST_PAYLOAD + ETH_HLEN + NET_IP_ALIGN);
-	if (!skb) {
-		en_err(priv, "-LOOPBACK_TEST_XMIT- failed to create skb for xmit\n");
+	if (!skb)
 		return -ENOMEM;
-	}
+
 	skb_reserve(skb, NET_IP_ALIGN);
 
 	ethh = (struct ethhdr *)skb_put(skb, sizeof(struct ethhdr));