[SK_BUFF]: Introduce skb_copy_to_linear_data{_offset}

To clearly state the intent of copying to 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@ghostprotocols.net>
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 62d5490..aec7ce7 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -786,15 +786,16 @@
 	*buf = buf_acquire(sz);
 	if (!(*buf))
 		return -ENOMEM;
-	memcpy((*buf)->data, (unchar *)hdr, hsz);
+	skb_copy_to_linear_data(*buf, hdr, hsz);
 	for (res = 1, cnt = 0; res && (cnt < num_sect); cnt++) {
 		if (likely(usrmem))
 			res = !copy_from_user((*buf)->data + pos,
 					      msg_sect[cnt].iov_base,
 					      msg_sect[cnt].iov_len);
 		else
-			memcpy((*buf)->data + pos, msg_sect[cnt].iov_base,
-			       msg_sect[cnt].iov_len);
+			skb_copy_to_linear_data_offset(*buf, pos,
+						       msg_sect[cnt].iov_base,
+						       msg_sect[cnt].iov_len);
 		pos += msg_sect[cnt].iov_len;
 	}
 	if (likely(res))