[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/hisax/isdnl2.c b/drivers/isdn/hisax/isdnl2.c
index cd3b5ad..3446f24 100644
--- a/drivers/isdn/hisax/isdnl2.c
+++ b/drivers/isdn/hisax/isdnl2.c
@@ -1293,7 +1293,8 @@
 		oskb = skb;
 		skb = alloc_skb(oskb->len + i, GFP_ATOMIC);
 		memcpy(skb_put(skb, i), header, i);
-		memcpy(skb_put(skb, oskb->len), oskb->data, oskb->len);
+		skb_copy_from_linear_data(oskb,
+					  skb_put(skb, oskb->len), oskb->len);
 		dev_kfree_skb(oskb);
 	}
 	st->l2.l2l1(st, PH_PULL | INDICATION, skb);