[SK_BUFF]: Introduce skb_copy_from_linear_data{_offset}

To clearly state the intent of copying from linear sk_buffs, _offset being a
overly long variant but interesting for the sake of saving some bytes.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
index be91505..387392c 100644
--- a/drivers/isdn/i4l/isdn_ppp.c
+++ b/drivers/isdn/i4l/isdn_ppp.c
@@ -1100,7 +1100,8 @@
 					goto drop_packet;
 				}
 				skb_put(skb, skb_old->len + 128);
-				memcpy(skb->data, skb_old->data, skb_old->len);
+				skb_copy_from_linear_data(skb_old, skb->data,
+							  skb_old->len);
 				if (net_dev->local->ppp_slot < 0) {
 					printk(KERN_ERR "%s: net_dev->local->ppp_slot(%d) out of range\n",
 						__FUNCTION__, net_dev->local->ppp_slot);
@@ -1902,7 +1903,9 @@
 		while( from != to ) {
 			unsigned int len = from->len - MP_HEADER_LEN;
 
-			memcpy(skb_put(skb,len), from->data+MP_HEADER_LEN, len);
+			skb_copy_from_linear_data_offset(from, MP_HEADER_LEN,
+							 skb_put(skb,len),
+							 len);
 			frag = from->next;
 			isdn_ppp_mp_free_skb(mp, from);
 			from = frag;