sock: remove one redundant SKB_FRAG_PAGE_ORDER macro

Both SKB_FRAG_PAGE_ORDER are defined to the same value in
net/core/sock.c and drivers/vhost/net.c.

Move the SKB_FRAG_PAGE_ORDER definition to net/core/sock.h,
as both net/core/sock.c and drivers/vhost/net.c include it,
and it seems a reasonable file to put the macro.

Signed-off-by: Yunsheng Lin <[e-mail]>
Acked-by: Jason Wang <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/vhost/net.c

···
 	       !vhost_vq_avail_empty(vq->dev, vq);
 }
 
-#define SKB_FRAG_PAGE_ORDER     get_order(32768)
-
 static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
 				       struct page_frag *pfrag, gfp_t gfp)
 {

include/net/sock.h

···
 extern __u32 sysctl_wmem_default;
 extern __u32 sysctl_rmem_default;
 
+#define SKB_FRAG_PAGE_ORDER	get_order(32768)
 DECLARE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
 
 static inline int sk_get_wmem0(const struct sock *sk, const struct proto *proto)

net/core/sock.c

···
 	}
 }
 
-#define SKB_FRAG_PAGE_ORDER	get_order(32768)
 DEFINE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
 
 /**