net: remove last caller of skb_tail_offset() and itself

Similar to the following commits:

commit 00f97da17a0c8d656d0c9 (netpoll: fix position of network header)
commit 525cebedb32a87fa48584 (pktgen: Fix position of ip and udp header)

using skb_tail_offset() seems not correct since the offset
is based on head pointer.

With the last caller removed, skb_tail_offset() can be killed
finally.

Cc: Thomas Graf <tgraf@suug.ch>
Cc: Daniel Borkmann <dborkmann@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1396,10 +1396,6 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 	skb->tail += offset;
 }
 
-static inline unsigned long skb_tail_offset(const struct sk_buff *skb)
-{
-	return skb->tail;
-}
 #else /* NET_SKBUFF_DATA_USES_OFFSET */
 static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
 {
@@ -1416,10 +1412,6 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 	skb->tail = skb->data + offset;
 }
 
-static inline unsigned long skb_tail_offset(const struct sk_buff *skb)
-{
-	return skb->tail - skb->head;
-}
 #endif /* NET_SKBUFF_DATA_USES_OFFSET */
 
 /*

net/ipv4/ipmr.c

@@ -945,7 +945,6 @@ static int ipmr_cache_report(struct mr_table *mrt,
 	struct igmpmsg *msg;
 	struct sock *mroute_sk;
 	int ret;
-	unsigned long tail_offset;
 
 #ifdef CONFIG_IP_PIMSM
 	if (assert == IGMPMSG_WHOLEPKT)
@@ -981,12 +980,7 @@ static int ipmr_cache_report(struct mr_table *mrt,
 
 	/* Copy the IP header */
 
-	tail_offset = skb_tail_offset(skb);
-	if (tail_offset > 0xffff) {
-		kfree_skb(skb);
-		return -EINVAL;
-	}
-	skb_set_network_header(skb, tail_offset);
+	skb_set_network_header(skb, skb->len);
 	skb_put(skb, ihl);
 	skb_copy_to_linear_data(skb, pkt->data, ihl);
 	ip_hdr(skb)->protocol = 0;	/* Flag to the kernel this is a route add */