lantiq: ltq-ptm: vr9: fix skb handling in ptm_hard_start_xmit()

Call skb_orphan(skb) to call the owner's destructor function and make
the skb unowned.

This is necessary to prevent sk_wmem_alloc of a socket from overflowing,
which leads to ENOBUFS errors on application level.

Signed-off-by: Martin Schiller <ms@dev.tdt.de>
(cherry picked from commit 996f02e5ba)

package/kernel/lantiq/ltq-ptm/Makefile

@@ -8,7 +8,7 @@ include $(TOPDIR)/rules.mk
 include $(INCLUDE_DIR)/kernel.mk
 
 PKG_NAME:=ltq-ptm
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_MAINTAINER:=John Crispin <john@phrozen.org>
 PKG_LICENSE:=GPL-2.0+

package/kernel/lantiq/ltq-ptm/src/ifxmips_ptm_vdsl.c

@@ -336,6 +336,9 @@ static int ptm_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
         dma_cache_wback((unsigned long)skb->data, skb->len);
     }
 
+    /* make the skb unowned */
+    skb_orphan(skb);
+
     *(struct sk_buff **)((unsigned int)skb->data - byteoff - sizeof(struct sk_buff *)) = skb;
     /*  write back to physical memory   */
     dma_cache_wback((unsigned long)skb->data - byteoff - sizeof(struct sk_buff *), skb->len + byteoff + sizeof(struct sk_buff *));