[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_ap.c b/drivers/net/wireless/hostap/hostap_ap.c
index 797d950..4ca8a27 100644
--- a/drivers/net/wireless/hostap/hostap_ap.c
+++ b/drivers/net/wireless/hostap/hostap_ap.c
@@ -1277,8 +1277,8 @@
 		return NULL;
 	}
 
-	memcpy(tmpbuf, skb->data + ap->crypt->extra_mpdu_prefix_len,
-	       WLAN_AUTH_CHALLENGE_LEN);
+	skb_copy_from_linear_data_offset(skb, ap->crypt->extra_mpdu_prefix_len,
+					 tmpbuf, WLAN_AUTH_CHALLENGE_LEN);
 	dev_kfree_skb(skb);
 
 	return tmpbuf;