[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/usb/atm/usbatm.c b/drivers/usb/atm/usbatm.c
index a076f73..d287c57 100644
--- a/drivers/usb/atm/usbatm.c
+++ b/drivers/usb/atm/usbatm.c
@@ -484,7 +484,7 @@
 		ptr[4] = 0xec;
 		ptr += ATM_CELL_HEADER;
 
-		memcpy(ptr, skb->data, data_len);
+		skb_copy_from_linear_data(skb, ptr, data_len);
 		ptr += data_len;
 		__skb_pull(skb, data_len);