[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/net/ax25/ax25_out.c b/net/ax25/ax25_out.c
index e66953c..92b517a 100644
--- a/net/ax25/ax25_out.c
+++ b/net/ax25/ax25_out.c
@@ -150,7 +150,7 @@
 				skb_reserve(skbn, frontlen + 2);
 				skb_set_network_header(skbn,
 						      skb_network_offset(skb));
-				memcpy(skb_put(skbn, len), skb->data, len);
+				skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
 				p = skb_push(skbn, 2);
 
 				*p++ = AX25_P_SEGMENT;
@@ -164,7 +164,7 @@
 				skb_reserve(skbn, frontlen + 1);
 				skb_set_network_header(skbn,
 						      skb_network_offset(skb));
-				memcpy(skb_put(skbn, len), skb->data, len);
+				skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
 				p = skb_push(skbn, 1);
 				*p = AX25_P_TEXT;
 			}