networking: make skb_push & __skb_push return void pointers

It seems like a historic accident that these return unsigned char *,
and in many places that means casts are required, more often than not.

Make these functions return void * and remove all the casts across
the tree, adding a (u8 *) cast only where the unsigned char pointer
was used directly, all done with the following spatch:

    @@
    expression SKB, LEN;
    typedef u8;
    identifier fn = { skb_push, __skb_push, skb_push_rcsum };
    @@
    - *(fn(SKB, LEN))
    + *(u8 *)fn(SKB, LEN)

    @@
    expression E, SKB, LEN;
    identifier fn = { skb_push, __skb_push, skb_push_rcsum };
    type T;
    @@
    - E = ((T *)(fn(SKB, LEN)))
    + E = fn(SKB, LEN)

    @@
    expression SKB, LEN;
    identifier fn = { skb_push, __skb_push, skb_push_rcsum };
    @@
    - fn(SKB, LEN)[0]
    + *(u8 *)fn(SKB, LEN)

Note that the last part there converts from push(...)[0] to the
more idiomatic *(u8 *)push(...).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wireless/intersil/orinoco/main.c

@@ -396,7 +396,7 @@ int orinoco_process_xmit_skb(struct sk_buff *skb,
 		memcpy(hdr.encap, encaps_hdr, sizeof(encaps_hdr));
 
 		/* Make room for the new header, and copy it in */
-		eh = (struct ethhdr *) skb_push(skb, ENCAPS_OVERHEAD);
+		eh = skb_push(skb, ENCAPS_OVERHEAD);
 		memcpy(eh, &hdr, sizeof(hdr));
 	}
 
@@ -1029,11 +1029,10 @@ static void orinoco_rx(struct net_device *dev,
 		/* These indicate a SNAP within 802.2 LLC within
 		   802.11 frame which we'll need to de-encapsulate to
 		   the original EthernetII frame. */
-		hdr = (struct ethhdr *)skb_push(skb,
-						ETH_HLEN - ENCAPS_OVERHEAD);
+		hdr = skb_push(skb, ETH_HLEN - ENCAPS_OVERHEAD);
 	} else {
 		/* 802.3 frame - prepend 802.3 header as is */
-		hdr = (struct ethhdr *)skb_push(skb, ETH_HLEN);
+		hdr = skb_push(skb, ETH_HLEN);
 		hdr->h_proto = htons(length);
 	}
 	memcpy(hdr->h_dest, desc->addr1, ETH_ALEN);