core, nfqueue, openvswitch: fix compilation warning

Stable commit "core, nfqueue, openvswitch: Orphan frags in
skb_zerocopy and handle errors", upstream commit
36d5fe6a, was not correctly backported
and missed to change a const 'from' parameter to non-const.  This
results in a new batch of warnings:

net/netfilter/nfnetlink_queue_core.c: In function ‘nfqnl_zcopy’:
net/netfilter/nfnetlink_queue_core.c:272:2: warning: passing argument 1 of ‘skb_orphan_frags’ discards ‘const’ qualifier from pointer target type [enabled by default]
  if (unlikely(skb_orphan_frags(from, GFP_ATOMIC))) {
  ^
In file included from net/netfilter/nfnetlink_queue_core.c:18:0:
include/linux/skbuff.h:1822:19: note: expected ‘struct sk_buff *’ but argument is of type ‘const struct sk_buff *’
 static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
                   ^
net/netfilter/nfnetlink_queue_core.c:273:3: warning: passing argument 1 of ‘skb_tx_error’ discards ‘const’ qualifier from pointer target type [enabled by default]
   skb_tx_error(from);
   ^
In file included from net/netfilter/nfnetlink_queue_core.c:18:0:
include/linux/skbuff.h:630:13: note: expected ‘struct sk_buff *’ but argument is of type ‘const struct sk_buff *’
 extern void skb_tx_error(struct sk_buff *skb);

Remove const from the 'from' parameter, the same as in the upstream
commit.

As far as I can see, this leaked into 3.10, 3.12, and 3.13 already.

Cc: Zoltan Kiss <zoltan.kiss@citrix.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org # v3.10, v3.12, v3.13
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/netfilter/nfnetlink_queue_core.c

@@ -236,7 +236,7 @@ nfqnl_flush(struct nfqnl_instance *queue, nfqnl_cmpfn cmpfn, unsigned long data)
 }
 
 static int
-nfqnl_zcopy(struct sk_buff *to, const struct sk_buff *from, int len, int hlen)
+nfqnl_zcopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
 {
 	int i, j = 0;
 	int plen = 0; /* length of skb->head fragment */