[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/decnet/dn_nsp_in.c b/net/decnet/dn_nsp_in.c
index d9498a1..4074a6e 100644
--- a/net/decnet/dn_nsp_in.c
+++ b/net/decnet/dn_nsp_in.c
@@ -362,7 +362,8 @@
 			u16 dlen = *skb->data;
 			if ((dlen <= 16) && (dlen <= skb->len)) {
 				scp->conndata_in.opt_optl = dn_htons(dlen);
-				memcpy(scp->conndata_in.opt_data, skb->data + 1, dlen);
+				skb_copy_from_linear_data_offset(skb, 1,
+					      scp->conndata_in.opt_data, dlen);
 			}
 		}
 		dn_nsp_send_link(sk, DN_NOCHANGE, 0);
@@ -406,7 +407,7 @@
 		u16 dlen = *skb->data;
 		if ((dlen <= 16) && (dlen <= skb->len)) {
 			scp->discdata_in.opt_optl = dn_htons(dlen);
-			memcpy(scp->discdata_in.opt_data, skb->data + 1, dlen);
+			skb_copy_from_linear_data_offset(skb, 1, scp->discdata_in.opt_data, dlen);
 		}
 	}