net/mac80211/rx.c: fix build error

older versions of gcc do not recognize that ieee80211_rx_h_mesh_fwding()
is unused when CONFIG_MAC80211_MESH is disabled:

  net/built-in.o: In function `ieee80211_rx_h_mesh_fwding':
  rx.c:(.text+0xd89af): undefined reference to `mpp_path_lookup'
  rx.c:(.text+0xd89c6): undefined reference to `mpp_path_add'

as this code construct:

        if (ieee80211_vif_is_mesh(&sdata->vif))
                CALL_RXH(ieee80211_rx_h_mesh_fwding);

still causes ieee80211_rx_h_mesh_fwding() to be linked in.

Protect these places with an #ifdef.

commit b0dee578 ("Fix modpost failure when rx handlers are not inlined.")
solved part of this problem - this patch is still needed.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mac80211/rx.c

@@ -1379,6 +1379,7 @@ ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx)
 	return RX_QUEUED;
 }
 
+#ifdef CONFIG_MAC80211_MESH
 static ieee80211_rx_result
 ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
 {
@@ -1453,7 +1454,7 @@ ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
 	else
 		return RX_DROP_MONITOR;
 }
-
+#endif
 
 static ieee80211_rx_result debug_noinline
 ieee80211_rx_h_data(struct ieee80211_rx_data *rx)
@@ -1780,8 +1781,10 @@ static void ieee80211_invoke_rx_handlers(struct ieee80211_sub_if_data *sdata,
 	/* must be after MMIC verify so header is counted in MPDU mic */
 	CALL_RXH(ieee80211_rx_h_remove_qos_control)
 	CALL_RXH(ieee80211_rx_h_amsdu)
+#ifdef CONFIG_MAC80211_MESH
 	if (ieee80211_vif_is_mesh(&sdata->vif))
 		CALL_RXH(ieee80211_rx_h_mesh_fwding);
+#endif
 	CALL_RXH(ieee80211_rx_h_data)
 	CALL_RXH(ieee80211_rx_h_ctrl)
 	CALL_RXH(ieee80211_rx_h_action)