mac80211: Put some code under MESH macro

In the function ieee80211_subif_start_xmit the logic related with
meshdrlen is under CONFIG_MAC80211_MESH macro, but in one place it isn't.
This is some update for this

Signed-off-by: Yuri Ershov <ext-yuri.ershov@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -1935,11 +1935,13 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
 		h_pos += encaps_len;
 	}
 
+#ifdef CONFIG_MAC80211_MESH
 	if (meshhdrlen > 0) {
 		memcpy(skb_push(skb, meshhdrlen), &mesh_hdr, meshhdrlen);
 		nh_pos += meshhdrlen;
 		h_pos += meshhdrlen;
 	}
+#endif
 
 	if (ieee80211_is_data_qos(fc)) {
 		__le16 *qos_control;