networking: make skb_put & friends 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 (skb_put, __skb_put and pskb_put) 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_put, __skb_put };
    @@
    - *(fn(SKB, LEN))
    + *(u8 *)fn(SKB, LEN)

    @@
    expression E, SKB, LEN;
    identifier fn = { skb_put, __skb_put };
    type T;
    @@
    - E = ((T *)(fn(SKB, LEN)))
    + E = fn(SKB, LEN)

which actually doesn't cover pskb_put since there are only three
users overall.

A handful of stragglers were converted manually, notably a macro in
drivers/isdn/i4l/isdn_bsdcomp.c and, oddly enough, one of the many
instances in net/bluetooth/hci_sock.c. In the former file, I also
had to fix one whitespace problem spatch introduced.

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

drivers/net/wireless/ath/wil6210/wmi.c

@@ -677,7 +677,7 @@ static void wmi_evt_eapol_rx(struct wil6210_priv *wil, int id,
 		return;
 	}
 
-	eth = (struct ethhdr *)skb_put(skb, ETH_HLEN);
+	eth = skb_put(skb, ETH_HLEN);
 	ether_addr_copy(eth->h_dest, ndev->dev_addr);
 	ether_addr_copy(eth->h_source, evt->src_mac);
 	eth->h_proto = cpu_to_be16(ETH_P_PAE);