[NET]: Remove CONFIG_HAVE_ARCH_DEV_ALLOC_SKB

skbuff.h has an #ifndef CONFIG_HAVE_ARCH_DEV_ALLOC_SKB to allow
architectures to reimplement __dev_alloc_skb.  It's not set on any
architecture and now that we have an architecture-overrideable
NET_SKB_PAD there is not point at all to have one either.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1066,7 +1066,6 @@ static inline void __skb_queue_purge(struct sk_buff_head *list)
 		kfree_skb(skb);
 }
 
-#ifndef CONFIG_HAVE_ARCH_DEV_ALLOC_SKB
 /**
  *	__dev_alloc_skb - allocate an skbuff for sending
  *	@length: length to allocate
@@ -1087,9 +1086,6 @@ static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
 		skb_reserve(skb, NET_SKB_PAD);
 	return skb;
 }
-#else
-extern struct sk_buff *__dev_alloc_skb(unsigned int length, int gfp_mask);
-#endif
 
 /**
  *	dev_alloc_skb - allocate an skbuff for sending