[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/net/wireless/hostap/hostap_hw.c b/drivers/net/wireless/hostap/hostap_hw.c
index 9003ff7..fb01fb9 100644
--- a/drivers/net/wireless/hostap/hostap_hw.c
+++ b/drivers/net/wireless/hostap/hostap_hw.c
@@ -1838,13 +1838,14 @@
 
 	/* skb->data starts with txdesc->frame_control */
 	hdr_len = 24;
-	memcpy(&txdesc.frame_control, skb->data, hdr_len);
+	skb_copy_from_linear_data(skb, &txdesc.frame_control, hdr_len);
  	fc = le16_to_cpu(txdesc.frame_control);
 	if (WLAN_FC_GET_TYPE(fc) == IEEE80211_FTYPE_DATA &&
 	    (fc & IEEE80211_FCTL_FROMDS) && (fc & IEEE80211_FCTL_TODS) &&
 	    skb->len >= 30) {
 		/* Addr4 */
-		memcpy(txdesc.addr4, skb->data + hdr_len, ETH_ALEN);
+		skb_copy_from_linear_data_offset(skb, hdr_len, txdesc.addr4,
+						 ETH_ALEN);
 		hdr_len += ETH_ALEN;
 	}