[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/hysdn/hycapi.c b/drivers/isdn/hysdn/hycapi.c
index b2ae4ec..4433ce0 100644
--- a/drivers/isdn/hysdn/hycapi.c
+++ b/drivers/isdn/hysdn/hycapi.c
@@ -398,7 +398,7 @@
 			_len = CAPIMSG_LEN(skb->data);
 			if (_len > 22) {
 				_len2 = _len - 22;
-				memcpy(msghead, skb->data, 22);
+				skb_copy_from_linear_data(skb, msghead, 22);
 				memcpy(skb->data + _len2, msghead, 22);
 				skb_pull(skb, _len2);
 				CAPIMSG_SETLEN(skb->data, 22);