ble_mesh: Fixes wrong subnet info used for Friend Clear

When Friend node tries to send Friend Clear message to other
Friend nodes, it should use the subnet information based on
the net_idx from friendship.

components/bt/esp_ble_mesh/mesh_core/friend.c

@@ -363,7 +363,7 @@ static int unseg_app_sdu_unpack(struct bt_mesh_friend *frnd,
     meta->is_dev_key = (app_idx == BLE_MESH_KEY_DEV);
     bt_mesh_net_header_parse(&buf->b, &meta->net);
     err = bt_mesh_app_key_get(meta->subnet, app_idx, &meta->key,
-                              &meta->aid, NODE, meta->net.ctx.addr);
+                              &meta->aid, 0x0, meta->net.ctx.addr);
     if (err) {
         return err;
     }
@@ -774,7 +774,7 @@ static void send_friend_clear(struct bt_mesh_friend *frnd)
         .send_ttl = BLE_MESH_TTL_MAX,
     };
     struct bt_mesh_net_tx tx = {
-        .sub  = &bt_mesh.sub[0],
+        .sub  = bt_mesh_subnet_get(frnd->net_idx),
         .ctx  = &ctx,
         .src  = bt_mesh_primary_addr(),
         .xmit = bt_mesh_net_transmit_get(),