mac80211: fix compile error when mesh is disabled

This fixes following compile error seen when
building mac80211 with mesh disabled:

.../backports-5.15.58-1/net/mac80211/agg-rx.c: In function 'ieee80211_send_addba_resp':
...backports-5.15.58-1/net/mac80211/agg-rx.c:255:17: error: 'struct sta_info' has no member named 'mesh'
  255 |         if (!sta->mesh)
      |                 ^~

sta_info.h shows this item as being optional based on flags:

	struct mesh_sta *mesh;

Guard the check to fix this.

Fixes: f96744ba6b ("mac80211: mask nested A-MSDU support for mesh")
Signed-off-by: Koen Vandeputte <[email protected]>

package/kernel/mac80211/patches/subsys/800-mac80211-mask-nested-A-MSDU-support-for-mesh.patch

@@ -18,13 +18,15 @@ Signed-off-by: David Bauer <[email protected]>
 
 --- a/net/mac80211/agg-rx.c
 +++ b/net/mac80211/agg-rx.c
-@@ -251,7 +251,9 @@ static void ieee80211_send_addba_resp(st
+@@ -251,7 +251,11 @@ static void ieee80211_send_addba_resp(st
  	mgmt->u.action.u.addba_resp.action_code = WLAN_ACTION_ADDBA_RESP;
  	mgmt->u.action.u.addba_resp.dialog_token = dialog_token;
  
 -	capab = u16_encode_bits(amsdu, IEEE80211_ADDBA_PARAM_AMSDU_MASK);
 +	capab = 0;
++#ifdef CONFIG_MAC80211_MESH
 +	if (!sta->mesh)
++#endif
 +		capab = u16_encode_bits(amsdu, IEEE80211_ADDBA_PARAM_AMSDU_MASK);
  	capab |= u16_encode_bits(policy, IEEE80211_ADDBA_PARAM_POLICY_MASK);
  	capab |= u16_encode_bits(tid, IEEE80211_ADDBA_PARAM_TID_MASK);